Upload
abdul-zahier-ismail
View
350
Download
12
Tags:
Embed Size (px)
Citation preview
CHAPTER 5: ORGANIC CHEMISTRY
5.1 Alkanes
5.2 Alkenes
5.3 Aromatic Hydrocarbons
5.4 Alcohols
5.5 Haloalkanes (Alkyl Halides)
5.6 Carbonyl Compounds
5.7 Carboxylic Acids
1
What Is Organic Chemistry?
Organic chemistry is a branch of chemistry that focuses on compounds that contain carbon
• except CO, CO2, carbonates, and carbides
Even though organic compounds only contain a few elements, the unique ways carbon atoms can attach together to form molecules leads to millions of different organic compounds
2
Tro: Chemistry: A Molecular Approach, 2/e
What’s So Special About Carbon?
Carbon atoms can do some unique things that other atoms cannot Carbon can bond to as many as four other atoms Bonds to carbon are very strong and nonreactive Carbon atoms can attach together in long chains Carbon atoms can attach together to form rings Carbon atoms can form single, double, or triple bonds
3
Tro: Chemistry: A Molecular Approach, 2/e
What’s Special About Organic Compounds?
Organic compounds tend to be molecular
Mainly composed of just six nonmetallic elements• C, H, O, N, S, and P
Compounds found in all three states• solids, liquids, and gases• solids tend to have low melting points
Solubility in water varies depending on which of the other elements are attached to C and how many there are• CH3OH is miscible with water; C10H21OH is insoluble
4
Tro: Chemistry: A Molecular Approach, 2/e
Carbon Bonding
Carbon forms four bonds When C has four single bonds, the
shape is tetrahedral When C has one triple + one single
or two double bonds, the shape is linear
When C has two single + one double bond, the shape is trigonal planar
5
Tro: Chemistry: A Molecular Approach, 2/e
Hydrocarbons Hydrocarbons contain only C and H
• aliphatic or aromatic Insoluble in water
• no polar bonds to attract water molecules Aliphatic hydrocarbons
• saturated or unsaturated aliphatics• saturated = alkanes, unsaturated = alkenes or alkynes
• may be chains or rings• chains may be straight or branched
Aromatic hydrocarbons
6
Tro: Chemistry: A Molecular Approach, 2/e
7
alkanes
Tro: Chemistry: A Molecular Approach, 2/e
Copyright © 2010 Pearson Education, Inc.
Alkanes
Saturated hydrocarbons (Aliphatic) • Hydrocarbons – Contain only C and H atoms.• Saturated – Only single bonds. • Aliphatic – “Fat” like. • Can be acyclic (no rings) or cyclic
(cycloalkanes).
Table 5.1 Numerical Roots for Carbon Chains and Branches
Number of C atomsRoots
1
2
3
4
5
6
8
7
9
10
meth-
eth-
prop-
but-
hex-
pent-
hept-
oct-
non-
dec-
PREFIX + ROOT + SUFFIX
Physical Properties of n–Alkanes
12
Tro: Chemistry: A Molecular Approach, 2/e
Physical Properties of Alkanes
Alkanes• Solubility – “Like dissolves like” • Alkanes are nonpolar, hydrophobic• They are soluble in nonpolar solvents and
insoluble in water.
Ways of depicting an alkane.
Formulas Molecular formulas : shows what kinds
of atoms are in the molecule, but not how they are bonded together
Structural formulas shows the bonding pattern in the molecule
15
Tro: Chemistry: A Molecular Approach, 2/e
AlkanesMethane, CH4
Ethane, CH3CH3
H
CH H
H
H
CH C
H
H
H
H
Copyright © 2010 Pearson Education, Inc.
AlkanesPropane, CH3CH2CH3
Butane, CH3CH2CH2CH3
H
CH C
H
H
C
H
H
H
H
H
CH C
H
H
C
H
H
C
H
H
H
H
Condensed Structural Formulas
Elements listed in order• central atom with attached atoms
Follow normal bonding patterns• shows position of multiple bonds
() used to indicate more than one identical group attached to same previous central atom• unless () group listed first in which case
attached to next central atom
18
Tro: Chemistry: A Molecular Approach, 2/e
Example – Write the structural and condensed formula for the straight chain alkane C8H18
Connect the C atoms in a row• Carbon backbone
Add H to complete four bonds on each C.• middle C gets 2 Hs • end C gets 3 Hs
The condensed formula has the H attached to each C written directly after it
19
Tro: Chemistry: A Molecular Approach, 2/e
Alkanes
Pentane, CH3CH2CH2CH2CH3
Hexane, CH3CH2CH2CH2CH2CH3
Heptane, CH3CH2CH2CH2CH2CH2CH3
Octane, CH3CH2CH2CH2CH2CH2CH2CH3
Nonane, CH3CH2CH2CH2CH2CH2CH2CH2CH3
Decane, CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
Carbon Skeleton Formulas
Each angle, and beginning and end, represents a C atom H omitted on C
• included on functional groups Multiple bonds indicated
• double line is double bond, triple line is triple bond
21
Tro: Chemistry: A Molecular Approach, 2/e
Isomerism
Isomerism – The phenomenon whereby certain chemical compounds have structures that are different although the compounds possess the same elemental composition.
Isomers – Two or more chemical substances having the same elementary composition and molecular weight but differing in structure.
Structural isomers are isomers are also called Constitutional isomers
Isomerism
Consider C4H10
These structures are constitutional isomers
H
CH C
H
H
C
H
H
C
H
H
H
HC C
C
C
H
H
H HH
H
H HH H
Normal Butane Isobutane
Rotation about a Bond Is Not Isomerism
24
Tro: Chemistry: A Molecular Approach, 2/e
Possible Structural Isomers of Alkanes
fill in the H to give each carbon four bonds
26
Example 20.1: Write the structural formula and carbon skeleton formula for the 5 structural isomers of C6H14
Tro: Chemistry: A Molecular Approach, 2/e
Alkyl Groups
Names and Formulas of Alkyl Groups:
Formula Name Formula Name
CH3- methyl CH3CH2CH2CH2- butyl
CH3CH2- ethyl (CH3)2CHCH2- isobutyl
CH3CH2CH2- propyl CH3CH2CH(CH3)- sec-butyl
(CH3)2CH- isopropyl (CH3)3C- tert-butyl
AlkanesNames and Formulas of Alkyl Groups:
Formula Name Formula Name
CH3- methyl CH3CH2CH2CH2- butyl
CH3CH2- ethyl (CH3)2CHCH2- isobutyl
CH3CH2CH2- propyl CH3CH2CH(CH3)- sec-butyl
(CH3)2CH- isopropyl (CH3)3C- tert-butyl
Primary (1o) carbon
AlkanesNames and Formulas of Alkyl Groups:
Formula Name Formula Name
CH3- methyl CH3CH2CH2CH2- butyl
CH3CH2- ethyl (CH3)2CHCH2- isobutyl
CH3CH2CH2- propyl CH3CH2CH(CH3)- sec-butyl
(CH3)2CH- isopropyl (CH3)3C- tert-butyl
Secondary (2o) carbon
AlkanesNames and Formulas of Alkyl Groups:
Formula Name Formula Name
CH3- methyl CH3CH2CH2CH2- butyl
CH3CH2- ethyl (CH3)2CHCH2- isobutyl
CH3CH2CH2- propyl CH3CH2CH(CH3)- sec-butyl
(CH3)2CH- isopropyl (CH3)3C- tert-butyl
Tertiary (3o) carbon
IUPAC Rules for Naming Alkanes Select the longest continuous chain of carbon
atoms as the parent compound. Number the carbon atoms in the parent carbon
chain starting from the end closest to the first carbon atom that has an alkyl or other group.
Name the alkyl group and designate the position on the parent carbon chain by a number.
When the same alkyl group branch chain occurs more than once, indicate this repetition by a prefix (di-, tri-, tetra-, and so forth).
When several different alkyl groups are attached to the parent compound, list them in alphabetical order.
Example 1
CH2 CH
CH3
CH3CH2CH3parent alkane
alkyl group
12345
3-methylpentane
CH2 CH
CH3
CH3CH2CH3parent alkane
alkyl group
12345
3-methylpentane
Copyright © 2010 Pearson Education, Inc.
Example 1
CH2 CH
CH3
CH3CH2CH3parent alkane
alkyl group
12345
3-methylpentane
Copyright © 2010 Pearson Education, Inc.
Example 1
CH2 CH
CH3
CH3CH2CH3parent alkane
alkyl group
12345
2-methylpentane
Example 2
1 2 3 4CH3 CH CH CH3
CH3 CH3
2,3-dimethylbutane
CH3 CH2 C CH3
CH3
CH3
1234
2,2-dimethylbutane
Example 2
1 2 3 4CH3 CH CH CH3
CH3 CH3
2,3-dimethylbutane
CH3 CH2 C CH3
CH3
CH3
1234
2,2-dimethylbutane
Example 2
1 2 3 4CH3 CH CH CH3
CH3 CH3
2,3-dimethylbutane
CH3 CH2 C CH3
CH3
CH3
1234
2,2-dimethylbutane
Example 2
1 2 3 4CH3 CH CH CH3
CH3 CH3
2,3-dimethylbutane
CH3 CH2 C CH3
CH3
CH3
1234
2,2-dimethylbutane
Example 3
CH3 CH CH2 CH CH CH CH3
CH3
CH3
CH3
CH3
1
2
3
4
567
2,3,4,6-tetramethylheptane
Example 3
CH3 CH CH2 CH CH CH CH3
CH3
CH3
CH3
CH3
1
2
3
4
567
2,3,4,6-tetramethylheptane
Note: Number the chain so that the substituents get the lowest possible numbers.
Example 3
CH3 CH CH2 CH CH CH CH3
CH3
CH3
CH3
CH3
1
2
3
4
567
2,3,4,6-tetramethylheptane
Note: Number the chain so that the substituents get the lowest possible numbers.
Example 4
CH3 CH CH2 CH2 CH3
CH2 CH312
3 4 5 6
3-methylhexane
Examples
Caution: Be careful to choose the longest chain as the parent alkane.
CH3 CH CH2 CH2 CH3
CH2 CH312
3 4 5 6
3-methylhexane
Examples
Caution: Be careful to choose the longest chain as the parent alkane.
CH3 CH CH2 CH2 CH3
CH2 CH312
3 4 5 6
3-methylhexane
Examples
123456CH3 CH2 CH2 CH2 C CH CH CH3
CH3CH3
CH2 CH3
Cl
78
3-chloro-4-ethyl-2,4-dimethyloctane
Examples
123456CH3 CH2 CH2 CH2 C CH CH CH3
CH3CH3
CH2 CH3
Cl
78
3-chloro-4-ethyl-2,4-dimethyloctane
Example 4
Note: Substituents are listed in alphabetical order.
123456CH3 CH2 CH2 CH2 C CH CH CH3
CH3CH3
CH2 CH3
Cl
78
3-chloro-4-ethyl-2,4-dimethyloctane
Draw the Compounds
3-ethylpentane
2,2,4-trimethylpentane
Draw the Compounds
3-ethylpentane
2,2,4-trimethylpentane
CH3 CH2 CH2 CH2 CH3
1 2 3 4 5
CH2 CH3
Draw the Compounds
3-ethylpentane
2,2,4-trimethylpentane
1 2 3 4 5CH2 CH3CH3 CH2 CH
CH2 CH3
Draw the Compounds
3-ethylpentane
2,2,4-trimethylpentane
1 2 3 4 5CH2 CH3CH3 CH2 CH
CH2 CH3
CH3 CH2 CH2 CH2 CH3
CH3
CH3 CH3
1 2 3 4 5
Draw the Compounds
3-ethylpentane
2,2,4-trimethylpentane
1 2 3 4 5CH2 CH3CH3 CH2 CH
CH2 CH3
CH3 C
CH3
CH3
CH2 CH2 CH3
CH3
1 2 3 4 5
Naming of Cycloalkanes
H2C CH2
CH2=
CH3
CH2H2C CH2
CH2CH
H2C
CH3
=
Naming of Cycloalkanes
H2C CH2
CH2=
CH3
CH2H2C CH2
CH2CH
H2C
CH3
=
Cyclopropane
Cycloalkanes
H2C CH2
CH2=
CH3
CH2H2C CH2
CH2CH
H2C
CH3
=
Cyclopropane
Methylcyclohexane
Cycloalkanes
H2C CH2
CH2=
CH3
CH2H2C CH2
CH2CH
H2C
CH3
=
Cyclopropane
Methylcyclohexane
Naming of Cycloalkanes
(CH2)5CH3
CH2
H2C CHCH2
CH2CH2CH2CH2CH2CH3
1-Cyclobutylhexane
Hexylcyclobutane
Cycloalkanes
1-Ethyl-2-methylcyclohexane
CH2H2C CH
CHCH2
H2C
CH2
CH3
CH3=
1
23
4
5
6
Name the Following Compounds
Name the Following Compounds
Methylcyclopropane 1,1-Dimethylcyclohexane
1,2-Dimethylcyclopentane 3-Cyclopropylpentane
Geometric Isomerism in Cycloalkanes
Geometric isomers have the same molecular formula but a different orientation in space that cannot be overcome by rotation around a bond.
1,2-Dimethylcyclopentane:
Geometric Isomerism in Cycloalkanes
1,2-Dimethylcyclopentane:
H3C CH3
H3C CH3
H H
H3C H
H CH3
1,2-dimethylcyclopentane
cis-1,2-dimethylcyclopentane trans-1,2-dimethylcyclopentane
Geometric Isomerism in Cycloalkanes
Geometric isomers have the same molecular formula and the same order of attachment but a different orientation in space that cannot be overcome by rotation around a bond.
1,2-Dimethylcyclopentane:
H3C CH3
H3C CH3
H H
H3C H
H CH3
1,2-dimethylcyclopentane
cis-1,2-dimethylcyclopentane trans-1,2-dimethylcyclopentane
Geometric Isomerism in Cycloalkanes
Name the following compounds:
C
CCH
H3CH
CH3H
H
H3C
H H
C CH3
CH3H3C
H H
H H
H
H H
H
Copyright © 2010 Pearson Education, Inc.
Geometric Isomerism in CycloalkanesName the following compounds:
C
CCH
H3CH
CH3H
H
H3C
H H
C CH3
CH3H3C
H H
H H
H
H H
H
trans-1,2-dimethylcyclopropanecis-1-tert-butyl-4-methylcyclohexane
Reactions of Hydrocarbons
All hydrocarbons undergo combustion
Combustion of butane
2 CH3CH2CH2CH3(g) + 13 O2(g) → 8 CO2(g) + 10 H2O(g)
66
Tro: Chemistry: A Molecular Approach, 2/e
Alkane Reactions
Substitution Reaction
• replace H with a halogen atom
• initiated by addition of energy in the form of heat or ultraviolet light
• to start breaking bonds
• generally get multiple products with multiple substitutions through chain reactions
67
Tro: Chemistry: A Molecular Approach, 2/e
Substitution Reaction
Chlorination of Methane Methane reacts with chlorine in the presence of heat or
light to produce a mixture of products through a sequence of substitution reactions in which the H atoms are successively replaced by Cl atoms.
CH4 + Cl2 heat or light CH3Cl + HCl
Cl2
CH2Cl2 + HCl
CH3Cl , chloromethane Cl2
CH2Cl2 , dichloromethane CHCl3 + HCl
CHCl3 , trichloromethane Cl2
CCl4 , tetracloromethane CCl4 + HCl
Free Radical Substitution
The breaking of a covalent bond so that each atom retains one of the shared electrons will produce two free radicals.
Free radicals are very reactive. They are intermediates in reaction mechanism.
The substitution reactions of alkanes follow the free radical mechanism, which involved three major steps:
1. Initiation: Initial production of free radicals
2. Propagation: Free radicals attack molecules to produce another free radical
3. Termination: Two free radicals combine to form a molecule
Mechanism of Free Radical substitution1. Chlorination of methane starts with the production of Cl free radicals (Cl
atoms)
Cl2 hv Cl∙ + Cl∙
2. The Cl free radical attacks the CH4 molecule to give a methyl free radical, CH3∙ and HCl.
CH4 + Cl∙ CH3∙ + HCl
The methyl free radical reacts with Cl2 to give chloromethane.
CH3∙ + Cl2 CH3Cl + Cl∙
Subsequent reactions produce various alkyl free radicals which lead to the formation of the other substitution products.
3. Reaction stops when free radicals combine
CH3∙ + Cl∙ CH3Cl
CH3∙ + CH3∙ CH3CH3 (by product)
Unsaturated Hydrocarbons
Unsaturated hydrocarbons have one or more C=C double bonds or CC triple bonds
Unsaturated aliphatic hydrocarbons that contain C=C are called alkenes• the general formula of a monounsaturated chain alkene is
CnH2n
Unsaturated aliphatic hydrocarbons that contain CC are called alkynes• the general formula of an alkyne with one triple bond is
CnH2n−2
71
Tro: Chemistry: A Molecular Approach, 2/e
Alkenes
Also known as olefins Aliphatic, unsaturated
• C=C double bonds Formula for one double bond = CnH2n
• subtract 2 H from alkane for each double bond Trigonal shape around C
• flat Polyunsaturated = many double bonds
72
Tro: Chemistry: A Molecular Approach, 2/e
Naming Alkenes and Alkynes
Change suffix on main name from -ane to -ene for base name of alkene, or to -yne for the base name of the alkyne
Number chain from end closest to multiple bond Number in front of main name indicates first
carbon of multiple bond
73
Tro: Chemistry: A Molecular Approach, 2/e
Alkenes
ethene = ethylene propene = propylene
produced by ripening fruit
C CH
H H
HC C
H
H CH3
H
used to make polyethylene used to make polypropylene74
Tro: Chemistry: A Molecular Approach, 2/e
75
Tro: Chemistry: A Molecular Approach, 2/e
Nomenclature of Alkenes
Find the longest carbon chain. Number the carbons such that the functional
group, here the double bond, gets the lowest possible number.
Substituents are cited before the parent longest chain, along with a number indicating its position at the chain.
Nomenclature of Alkenes
1
2
3
4
2-buteneHigh electron density
Low electron density
1
2
3
4
Electrostatic map showshigh electron densityat double bond
Copyright © 2010 Pearson Education, Inc.
Nomenclature of Alkenes
5-methyl-3-heptene
CH3
H3C
H3C
H
H
7
1
2
3
4
56
6 5 43
2
17
Copyright © 2010 Pearson Education, Inc.
Nomenclature of Alkenes
2-methyl-3-hexene
H3CCH3
CH3
6
5
4
3
2
1
6 5 43
21
Name the Alkene
1. Find the longest, continuous C chain that contains the double bond and use it to determine the base name
Because the longest chain with the double bond has6 C the base name is hexene
80
Tro: Chemistry: A Molecular Approach, 2/e
2. Identify the substituent branches
Name the Alkene
there are 2 substituentsone is a 1 C chain, called methyl
the other one is a 2 C chain, called ethyl
81
Tro: Chemistry: A Molecular Approach, 2/e
b) then assign numbers to each substituent based on the number of the main chain C it is attached to
Name the Alkene
1234
5 6
3. number the chain and substituents
a) determine the end closest to the double bond
• if double bond equidistant from both ends, number from end closest to the substituents
Tro: Chemistry: A Molecular Approach, 2/e
Name the Alkene
4. Write the name in the following ordera. substituent number of first alphabetical substituent –
substituent name of first alphabetical substituent – use prefixes to indicate multiple identical substituents
b. repeat for other substituentsc. number of first C in double bond – name of main chain
3–ethyl– 4–methyl– 2–hexene
83
1234
5 6
Tro: Chemistry: A Molecular Approach, 2/e
Practice – Name the following
3,4-dimethyl-3-hexene
12
3 4 5 6
84
Tro: Chemistry: A Molecular Approach, 2/e
Physical Properties of Alkenes
85
Tro: Chemistry: A Molecular Approach, 2/e
Geometric Isomerism Because the rotation around a double bond is highly restricted,
you will have different molecules if groups have different spatial orientation about the double bond
This is often called cis–trans isomerism When groups on the doubly bonded carbons are cis, they are on
the same side of the double bond When groups on the doubly bonded carbons are trans, they are
on opposite sides
86
Tro: Chemistry: A Molecular Approach, 2/e
cis/trans Isomers
R
H H
R H
R H
R
All substituents are on one side of bond
All substituents are on different sides
of bond
cis trans
Cis-Trans Isomerism
88
The cis and trans isomers are different molecules with different properties.
Tro: Chemistry: A Molecular Approach, 2/e
cis/trans Isomers
1
23
45
cis-2-pentene
1
23
4
5
1
2345
cis/trans Isomers
12
34
56
7 trans-3-heptene
12
345
67
12
34
5
6
7
cis/trans IsomersThe main chain determines cis/trans in the name
H3C
CH3
1
23
45
6
cis-3-methyl-2-hexene
H3C CH31
2 3
45
6trans-3-methyl-2-hexene
This compound is cisbut the two methylgroups are … trans to each other.
This compound is transbut the two methylgroups are … cis to each other.
NOTE: For more than two substituents, the cis/trans system cannot be used
Reactions of Alkenes
Alkenes are relatively more reactive than alkanes.The electron-rich double bond is the ‘active site’ or the functional group of the molecule .
Organic Functional Groups
ClassFunctional Group
Example
Alkene C C
CH3
H3C CH2Limonene
Reactions of Alkenes
Addition ReactionsAn addition reaction is a reaction in which an unsaturated molecule becomes saturated by the addition of a molecule across a multiple bond.
Addition reaction to a double bond:
C C + X Y C C
X Y
Types of Addition Reactions
Note: For some alkenes, heat or light may be required.
1. Catalytic Hydrogenation: Alkenes and hydrogen react in the presence of a catalystto form alkanes.
C2H4 + H2 Ni C2H6
2(a) Addition of Halogen in inert solventHalogens dissolved in an inert solvent such as carbon tetrachloride, react readily with alkenes at room temperature and even in the dark.
CH3 CH CH2 + Br2 inert solvent CH3CHBrCH2Br propene bromine 1,2-dibromopropane
Addition Reactions
2(b) Addition of Halogen in waterChlorine or bromine dissolved water reacts with alkene to produce halohydrin as the major product.
CH3 CH CH2 + Br2 water CH3CH(OH)CH2Br + CH3CHBrCH2Br
propene bromine bromohydrin 1,2-dibromopropane (major product) (minor product)
Note: In both reactions 2(a) and 2(b), the red-brown colour of the bromine solution will disappeared.In reaction 2(b), bromine water contains HBr and HOBr.
Br2(aq) + H2O(l) ⇄ HBr(aq) + HOBr(aq)
Addition Reactions
3. Addition of Halogen halides
Addition reaction of alkenes with hydrogen halides (HX) form haloalkanes (alkyl halides) Relative reactivity of HX towards alkenes increases in the order of HF < HCl < HBr < HI
CH2 CH2 + HBr CH3CH2Br ethene hydrogen bromoethane
bromide
Reactions of AlkenesAddition of HBr to Alkenes
C
CCH3
H
HBr(aq)
C
C
CH3
Br
HH
H2C C
CH2
CH3
CH3 HBr(aq)H2C C
CH3
CH2
BrH
CH3
Predicting Major and Minor Addition Products:
The Markovnikov’s rule
When an HX molecule is added to an unsymmetrical alkene,the X atom attaches itself to the C atom (of the double bond)which is more alkylated (having less H atoms), while the H atombonds to the adjacent C atom with larger number of H atoms (already bonded to it).
When an HX molecule is added to an unsymmetrical alkene, two possible products can be formed:
CH3CH CH2 + HBr CH3CHBrCH3 + CH3CH2CH2Br
propene 2-bromopropane 1-bromopropane
(major product) (minor product)
Electrophile and Nucleophile
An electrophile is a species (ion or molecule) which attacks electron-rich site of organic molecules such as double bonds.Electrophiles are Lewis acids (either positive ions or molecules with electron-deficient atom) Examples: HCl , H3O+
A nucleophile is a species (ion or molecule) which attacks electron-poor carbon atom of organic molecule, by donating electron-pair to the atom.Nucleophiles are Lewis bases, containing lone pair of electronsExamples: CH3NH2 H2OHO Cl
Reaction Mechanism: Electrophilic Addition
Hydrogen bromide is a strong acid and formshydronium ions, H3O+, and bromide, Br–, when dissolved in water.
electrophile
HBr + H2O Br + H3O
H3O+ is positively charged, thus it is electron deficient. It is electrophilic (electron-loving)
Reaction mechanism: Electrophilic attack
The hydronium ion reacts with the C=C bond,producing an electrophilic carbocation
Carbocation
CH2C
H2C
H3C
H3CCH2C
H2C
H3C
H3C
HO H
H
H
+ + H2O
Note: Another carbocation CH3CH2CH(CH3)C⁺H2 is also formed, but it is less stable.
Reaction mechanism:
Br– is rich in electrons. It is nucleophilic. Br– seeks for the electron-poor carbocation. The two species, electrophile and nucleophile, combineand form a new compound, 2-bromo-2-methylpropane
H2C C
CH2
CH3H
CH3
+ Br H2C
CH3
CH2
BrH
CH3
Note: Reaction of Br– with the other carbocation CH3CH2CH(CH3)C⁺H2 will produce the minor product, 1-bromo-2-methylpropane. This is the minor product as predicted by the Markovnikov’s rule.
2-bromo-2-methylpropane (Major product)
Electrophilic Addition: Summary of Mechanism
Step 1 reaches a carbocation “intermediate.” One new bond is formed.
Step 2 completes the reaction by forming a secondbond. Again, it is the interplay between positively charged (electrophilic) and negatively charged (nucleophilic) species.
Overall Mechanism of Electrophilic Addition
Summarizing our reaction, we realize it is a 2-step mechanism
HBr + H2O Br + H3O
STEP 1
STEP 2
CH2C
H2C
H3C
H3CCH2C
H2C
H3C
H3C
H
O H
H
H
+ + H2O
H2C C
CH2
CH3H
CH3
+ Br H2C
CH3
CH2
BrH
CH3
Addition Reactions
4. Addition with acidified water (H3O+) : Hydration of alkenes
Addition of H and OH groups from a water molecule to a double bond will produce an alcohol. The reaction is facilitated by using an acid as a catalyst.
CH3CH CH2 + H2O H2SO4 CH3CH(OH)CH3
2-propanol
Hydration of alkenes using concentrated H2SO4 followed by hydrolysis, would give the same results.
Unsaturation Tests for Alkenes
Alkenes or unsaturated organic compounds may be identified using simple lab tests
1. Br2 in inert solvent or dilute bromine water are yellow brown in colour. The solution is decolorised when added to an alkene (See: Addition reactions with halogens)
2. Reaction with cold, dilute, alkaline KMnO4 (Baeyer’s test)Alkenes are oxidised readily by the Baeyer’s reagent. The purple colour of the KMnO4 solution disappears, and a brown precipitate of Mn(IV) oxide appears. The organic product is a diol. CH3(CH2)6CHCH2 KMnO4 (aq), OH⁻ CH3(CH2)6CH(OH)CH2OH
1-nonene a diol
Unsaturation Tests for Alkenes
3. Reaction of Alkenes with hot, acidified KMnO4
Vigorous oxidation of alkenes results in the cleavage ofthe double bonds producing ketones, carboxylic acids or CO2
CH3CH CHCH2 CH3 KMnO4/H+
CH3COOH + CH3CH2COOH
carboxylic acids
In this reaction, the KMnO4 solution is decolourised. By identifying the products, the position of the double bond in the alkene can be determined.
Alkynes
Aliphatic, unsaturated CC triple bond Formula for one triple bond = CnH2n−2
• subtract 4 H from alkane for each triple bond
Linear shape Internal alkynes have both triple bond carbons
attached to C Terminal alkynes have one carbon attached to H
109
Tro: Chemistry: A Molecular Approach, 2/e
Alkynes
both used in welding torches
110
Tro: Chemistry: A Molecular Approach, 2/e
111
Tro: Chemistry: A Molecular Approach, 2/e
Name the Alkyne
1. Find the longest, continuous C chain that contains the triple bond and use it to determine the base name
Because the longest chain with the triple bond has 7 C the base name is heptyne
112
Tro: Chemistry: A Molecular Approach, 2/e
2. Identify the substituent branches
Name the Alkyne
there are 2 substituentsone is a 1 C chain, called methylthe other one is called isopropyl
113
Tro: Chemistry: A Molecular Approach, 2/e
Name the Alkyne
114
1234567
3. number the chain and substituents
a. determine the end closest to the triple bond if triple bond equidistant from both ends, number from
end closest to the substituents
b. then assign numbers to each substituent based on the number of the main chain C it is attached to.
Tro: Chemistry: A Molecular Approach, 2/e
Name the Alkyne
4. write the name in the following ordera) substituent number of first alphabetical substituent –
substituent name of first alphabetical substituent – use prefixes to indicate multiple identical substituents
b) repeat for other substituentsc) number of first C in triple bond – name of main chain
4–isopropyl–6–methyl–2–heptyne
1234567
115
Tro: Chemistry: A Molecular Approach, 2/e
Practice – Name the Following
3,3-dimethyl-1-pentyne
123
4 5
116
Tro: Chemistry: A Molecular Approach, 2/e
Examples of Naming Alkynes
117
Tro: Chemistry: A Molecular Approach, 2/e
Examples of Naming Alkenes
118
Tro: Chemistry: A Molecular Approach, 2/e
Alkyne Reactions:
Hydrogenation = adding H2
• alkene or alkyne + H2 → alkane
• generally requires a catalyst
Halogenation = adding X2
Hydrohalogenation = adding HX• HX is polar
• when adding a polar reagent to a double or triple bond, the positive part attaches to the carbon with the most H’s
119
Tro: Chemistry: A Molecular Approach, 2/e
Alkynes undergo many reactions similar to alkenes:
Alkynes: Reactions
C CH3C CH3
HBr
H3C
H H3C
Alkynes are electron-rich molecules, thus also electrophilic addition takes place.
2-butyne vinyl-carbocation
Alkynes: Reactions
H3C
H H3C
+ Br
H3C
H
Br
CH3
After the addition of the nucleophile we obtain an alkenethat still can be attacked by an electrophile.
Alkynes: Reactions
H3C
H
Br
CH3 HBr
H3C
CH3
Br
HH
Formation of a second carbocation
Alkynes: Reactions
H3C
CH3
Br
HH
H3C
CH3
Br
HH Br
H3C
CH3
Br
Br
HH
Both nucleophiles end up on the same carbon.
Aromatic Compounds
An aromatic compound is a compound that contains a benzene ring in its molecule.Aromatic hydrocarbons are also called arenes
The Structure of benzene (C6H6)
Derivatives of benzene: Other compounds have the benzene ring with other groups substituted for some of the Hydrogens
Aromatic Hydrocarbons
Aromatic hydrocarbons contain a ring structure that seems to have C=C, but doesn’t behave that way
The most prevalent example is benzene.• C6H6
• Other compounds have the benzene ring with other groups substituted for some of the Hydrogens
125
Tro: Chemistry: A Molecular Approach, 2/e
Naming Monosubstituted Benzene Derivatives
halogen substituent
Names of a common derivatives
126
Tro: Chemistry: A Molecular Approach, 2/e
Naming Benzene as a Substituent
When the benzene ring is not the base name, it is called a phenyl group
127
Tro: Chemistry: A Molecular Approach, 2/e
Naming Disubstituted Benzene Derivatives
Number the ring starting at attachment for first substituent, then move toward second
• order substituents alphabetically
• use “di” if both substituents are the same
128
Tro: Chemistry: A Molecular Approach, 2/e
Practice – Name the Following
1-chloro-4-fluorobenzene 1,3-dibromobenzeneor meta-dibromobenzene
or m-dibromobenzene
129
Tro: Chemistry: A Molecular Approach, 2/e
Polycyclic Aromatic Hydrocarbons
Contain multiple benzene rings fused together
• fusing = sharing a common bond
130
Tro: Chemistry: A Molecular Approach, 2/e
Alcohols
Aliphatic, hydroxy compounds• Contain hydroxy functional groups (—OH)
General formula = CnH2n + 1OH (n ≥ 1)
Considered as derivatives of alkanes with H atoms replacedby OH groups.
R—H R—OHalkane alcohol
131
Tro: Chemistry: A Molecular Approach, 2/e
Functional Groups Other organic compounds are hydrocarbons in which
functional groups have been substituted for hydrogens A functional group is a group of atoms that show a
characteristic influence on the properties of the molecule• generally, the reactions that a compound will perform are
determined by what functional groups it has
• because the kind of hydrocarbon chain is irrelevant to the reactions, it may be indicated by the general symbol R
CH3—OH
R group functional group
132
Tro: Chemistry: A Molecular Approach, 2/e
133
Tro: Chemistry: A Molecular Approach, 2/e
Alcohols R—OH Ethanol = CH3CH2OH
• grain alcohol = fermentation of sugars in grains
• alcoholic beverages• proof number = 2x percentage of alcohol
• gasohol Isopropyl alcohol = (CH3)2CHOH
• 2-propanol• rubbing alcohol• poisonous
Methanol = CH3OH• wood alcohol = thermolysis of wood• paint solvent• poisonous
134
Tro: Chemistry: A Molecular Approach, 2/e
Naming Alcohols
Identify main chain containing OH group Number main chain C atoms from end closest to
the OH group Give base name ol ending and place number of C
on chain where OH is attached in front Name all substituents present and write the lowest
possible numbers List substituents in alphabetical order
135
Tro: Chemistry: A Molecular Approach, 2/e
Copyright © 2010 Pearson Education, Inc.
Naming Alcohols
CH3CH2CH2CH2CHCH2OH
CH2CH2CH3C
C
Give the IUPAC name of the alcohol:
Copyright © 2010 Pearson Education, Inc.
Naming Alcohols
CH3CH2CH2CH2CHCH2OH
CH2CH2CH3
1 2 3 4 5
6 7 8
1 2 3 4 5 6
CC
Determine longest chain with OHBlue chain is longer; however,Red chain contains OH
Naming Alcohols
CH3CH2CH2CH2CHCH2OH
CH2CH2CH3
123456
1 2 3
CC
Determine longest chain with OHBlue chain is longer; however,Red chain contains OH
Name: 2-propyl-1-hexanol
Notice that numbering starts at alcohol group
Classification of alcohols
Based on the number of alkyl groups (R) bonded to the C atom that carries the -OH group, alcohols are classified into three types:
Primary, Secondary, and Tertiary
CH2 OHR CH OHR
R'C OHR
R
R10 20 30
Reactions of Alcohols
140
Nucleophilic substitution: 1. Reaction with H ─X
CH3─OH + HCl CH3Cl + H2O
2. Reaction with PCl3
CH3─ CH2OH CH3─ CH2ClPCl3
Tro: Chemistry: A Molecular Approach, 2/e
Cl⁻ acts as a nucleophile, replacing –OH group
Note: Conversion of an alcohol to a haloalkane can also be done by using PCl5 or SOCl2 (thionyl chloride) instead of PCl3
Substitution Reaction
HOHI
I + H2O
cyclohexanol iodocyclohexane
OHHCl
Cl + H2O
1-propanol 1-chloropropane
**Substitution reactions may be used to convert an alcohol to a haloalkane
Elimination Reaction (Dehydration)
Elimination of water, dehydration, is commonly obtained using sulfuric acid (H2SO4) as a catalyst.
H3C
CH3
OH H2SO4
H3CHC CHCH3 + H2O
**Dehydration can be used to convert alcohols to alkenes
Elimination (Dehydration)
The ease of dehydration follows the order:
OH
R
R
R
OH
R
H
R
OH
H
R
H> >
Elimination reaction
OH 1-pentene (minor product)
2-pentanol
2-pentene (major product)
Saytzeff’s rule: For elimination reaction that produces more than one alkenes, the alkene with more than one alkyl substituents in the double bond is the predominant product.
Reactions of Alcohols
145
3. Oxidation: Dehydrogenation
CH3CH2OH CH3CHO CH3COOH −2 H −2 H
Tro: Chemistry: A Molecular Approach, 2/e
Typical oxidizing agents are:
1. Acidified potassium dichromate (K2Cr2O7) or chromic acid H2CrO4
2. Acidified potassium permanganate (KMnO4)
Oxidation of Alcohols
Remember, we distinguish three types of alcohols:
RO
H
aldehyde
RO
R'ketone
Dehydrogenation (oxidation) is possible for 10 and 20 leading to aldehydes and ketones, respectively. 30 resists oxidation
CH2 OHR CH OHR
R'C OHR
R
R10 20 30
10 alc. 20 alc.
Oxidation of Alcohols
Aldehydes can be further oxidized to carboxylic acids.
RO
HR
O
OH
aldehyde acid
Oxidation of alcohols
OH
H2CrO4
O
cyclopentanol cyclopentanone
OHH2CrO4 O
H
H2CrO4
OH
O
butanolbutanal
butanoic acid
Reaction of alcohols with very active metals
2 CH3─OH + 2 K 2 CH3O−K+ + H2 potassium methoxide
2 CH3CH2─OH + 2 Na 2 CH3CH2O−Na+ + H2 sodium ethoxide
Tests to Distinguish Classes of Alcohols
Two simple lab tests can be used to distinguish between Primary, secondary and tertiary alcohols:
1. Lucas test: The alcohols is shaken with a solution of ZnCl2 in concentrated HCl. (Lucas reagent)
For a 30 alcohol , the solution turns cloudy almost immediately.
For a 20 alcohol , cloudiness* observed in about 5 minutes.
10 alcohol shows no cloudiness.*Cloudiness is due to the formation of alkyl halide
Lucas Reagent Test
155
OH Cl ZnCl2 / HCl
2-2-butanol 2-chloro-2-methylbutane
(a 30 alcohol) (Cloudiness appears immediately)
ZnCl2 / HCl
OH Cl 2-pentanol 2-chloropentane (a 20 alcohol) (cloudiness appears in a few minutes)
No reaction
OH propanol (a 10 alcohol)
Tests to Distinguish Classes of Alcohols
2. Oxidation test:
Only 10 and 20 alcohols are oxidised by hot acidified KMnO4 or hot acidified K2Cr2O7 solution.
10 and 20 alcohols decolourise the KMnO4 solution, whereas the colour of the K2Cr2O7 solution changes from orange to green.
No reaction for 30 alcohols.
Tests to Distinguish Classes of Alcohols
3. Iodoform test
Ethanol and 20 alcohols with methyl alcohol group
H
CH3C (methyl alcohol group)
OHreacts with iodine in aqueous NaOH to produce pale yellowsolid of iodoform (CHI3).
CH3CH2OH I2 / NaOH CHI3
Triiodomethane (iodoform) yellow precipitate
Haloalkanes Also called alkyl halides General formula = CnH2n + 1X (n ≥ 1), or R‒ X
X = F, Cl, Br or I Functional Group:
‒ C ‒ X
Nomenclature
Name as derivative of alkane:
replacing the H atom(s) by halogen atom(s)
Positions of halogen atoms are indicated by thenumber assigned to the C atom to which it is attached
CH3CH2Br (CH3)3CI IUPAC name: bromoethane 2-iodo-2-methylpropaneCommon name: ethyl bromide tert-butyl iodide
Nomenclature
Name the compounds:
a) CH3CH2CH (CH3)CH2CHCH3
Cl
2-chloro-4-methylhexane
b) Br CH3
1-bromo-3-methylcyclopentane
Reactions of Haloalkanes
The C — X bonds in haloalkanes are polar bonds
The C atom is electron-poor, it attracts nucleophiles δ+ δ-
— C — X
Reactions of haloalkanes include:
1. Elimination2. Nucleophilic substitution3. Grignard reactions
Reactions of haloalkanes
Elimination Reaction: Dehydrohalogenation adjecent H and X atoms are removed to produce a
double bond (an alkene)
R—CH —CH2 R—CH CH2 + HX
H X alkene
Example: When bromoethane is heated with a solution of NaOH in ethanol under reflux, elimination of HBr occurs and ethene is produced.
H—CH —CH2 Ethanolic NaOH H—CH CH2 + HBr
H Br ethene
Reactions of haloalkanes
Dehydrohalogenation of alkyl halides follows the Saytzeff’s rule. When more than one alkenes can be formed, the alkene with double bond containing more alkyl substituents is the predominant product.
Example: Dehydrohalogenation of 2-iodobutane by refluxing with alcoholic KOH produces:
2-butene
H H H CH3CH CH—CH3 (major product)
CH3C—C—CH
H I H CH3CH2CH CH2 (minor product)
2-iodobutane 1-butene
Reactions of Haloalkanes
Nucleophilic Substitution Reactions
The reaction of alkyl halides with hydroxide ion in aqueous solution is a nucleophilic substitution reaction. The OH− acts as a nucleophile, relpacing the halogen atom to form an alcohol
H H
CH3 — C — Cl + OH − heat CH3 — C — OH
H H
Chloroethane ethanol
Reactions of Haloalkanes
Grignard Reactions
When an alkyl halide reacts with a metal such as Mg, an organometallic compound, called the grignard reagent , is produced.
R — X + Mg ether R — Mg — X
a Grignard reagent
The reaction must be carried out in the absence of water. Diethyl ether is often used as the solvent.
Reactions of Haloalkanes
The Grignard reagent is a very strong Lewis base. The alkyl portion of the molecule can act as a nucleophile. It reacts rapidly with molecules having acidic H atom including water, producing an alkane.
δ‒ δ+
CH3CH2— Mg—Br + H — OH CH3CH3 + BrMgOH
ethylmagnesium bromide water ethane
Grignard reagent is primarily used in the synthesis of alcohols. It reacts with aldehyde or ketone to produce alcohols of the desired structures. (See: Reactions of Aldehyde and Ketone)
Aldehydes and Ketones Contain the carbonyl group Aldehydes = at least 1 side H Ketones = both sides R groups Many aldehydes and ketones have
pleasant tastes and aromas Formaldehyde : H2C=O
• pungent gas• formalin = a preservative• wood smoke, carcinogenic
Acetone : CH3C(=O)CH3
• nail-polish remover
163
Tro: Chemistry: A Molecular Approach, 2/e
Aldehyde Odors and Flavors
164
butanal = butter
vanillin = vanilla
benzaldehyde = almonds
cinnamaldehyde = cinnamon
Tro: Chemistry: A Molecular Approach, 2/e
acetophenone = pistachio
carvone = spearmint
ionone = raspberries
muscone = musk
Ketone Odors and Flavors
165
Tro: Chemistry: A Molecular Approach, 2/e
Naming Aldehydes and Ketones Main chain contains C=O group Number the main chain from end closest to C=O For aldehydes, give base name al ending
• always on C1
For ketones, give base name one ending and according to number of C on chain where C=O attached
166
Tro: Chemistry: A Molecular Approach, 2/e
169
Reactions of Aldehydes and Ketones
The carbonyl group in aldehydes and ketones has a constant polarity.
C=O δ+ δ−
The O atom attracts electrophiles; the C atom attracts nucleophiles
Addition of HCN to C=O
168
polar molecule HCN adds across the C=O, with the positive part (H) attaching to O; the nucleophile CN attaching to C atom
−
Tro: Chemistry: A Molecular Approach, 2/e
2-hydroxypropanenitrile
Reduction Reactions of Aldehydes and Ketones
Aldehydes and ketones are generally synthesized by the oxidation of alcohols
Therefore, reduction of an aldehyde or ketone results in an alcohol.
Common reducing agents are H2 with a Ni catalyst, NaBH4, and LiAlH4
169
Tro: Chemistry: A Molecular Approach, 2/e
Catalytic hydrogenation reactions:
RCHO H2/Ni or LiAlH4 RCH2OH (a 10 alcohol)
O OH
R —C — R’ H2/Ni or LiAlH4 R — C — R’ (a 20 alcohol)
Oxidation of Aldehydes
Aldehydes are easily oxidised using mild oxidising agents Ketones would not oxidise even using strong oxidising agents
A. Tollen’s reagent (Silver mirror test)
Tollen’s reagent is a solution of silver nitrate in ammonium hydroxide containing the silver complex Ag(NH3)2
+,
An aldehyde is oxidised by Ag(NH3)2 + , which is reduced to
metallic Ag. Ketones give no reaction.
RCHO + 2Ag(NH3)2+ + OH‒ RCOO‒ + 2Ag + 2NH4
+ + 2NH3
173
Oxidation of Aldehydes
B. Fehling’s reagent test for aldehydes
Fehling’s reagent consists of a basic solution of Cu(II) complex with a deep blue colour.
It oxidises aldehyde, and is itself reduced to a brick-red deposit of Cu(I) oxide. Ketones give no reaction.
RCHO + 2Cu2+(complex) + 5OH‒ RCOO‒ + Cu2O + 3H2O
*Aldehydes also decolourise acidified solution of KMnO4
173
C. Iodoform test for ethanal, CH3CHO, and methyl Ketones
A methyl ketone has a CH3 group attached to the carbonyl carbon. O
R — C — CH3 R = H or any alkyl group
The reagent consists of an aqueous solution of I2 in NaOH or KOH. On reacting with ethanal, a yellow precipitate of triiodomethane (iodoform) appears.
CH3CHO + 3 I2 + NaOH CH3COONa + CH3I + 3HI
Note: ethanol, CH3CH2OH or a sec. alcohol with the group CH3CH —
also give positive iodoform tests. OH
174
Reactions of Aldehydes and Ketones
Reaction of Grignard Reagents (RMgX)
a) With methanal gives a 10 alcohol
RMgX + HCHO ether R— CH2OMgX H2O/H+ RCH2OH (a 10 alcohol)
b) With other aldehydes give 20 alcohol
RMgX + R′CHO ether R′— CHOMgX H2O/H+ R′— CHOH
R R
(a 20 alcohol)
With ketones gives 30 alcohol
O OMgX OH
RMgX + R′ — C — R″ ether R′—C—R″ H2O/H+ R′—C—R″
R R
(a 30 alcohol)
175
Carboxylic Acids
174
• CnH2n + 1COOH (n ≥ 0)
• RCOOH
• Sour tasting
• Weak acids• Citric acid
found in citrus fruit
• Ethanoic acid = acetic acid, CH3COOH vinegar
• Methanoic acid = formic acid, HCOOH insect bites and stings
Tro: Chemistry: A Molecular Approach, 2/e
Synthesis of Carboxylic Acids
Made by the oxidation of aldehydes and alcohols
175
Tro: Chemistry: A Molecular Approach, 2/e
Naming Carboxylic Acids
Carboxylic acid group always on end of main chain
• has highest naming precedence of functional groups C of group always C1
• position not indicated in name Change ending to oic acid
176
Tro: Chemistry: A Molecular Approach, 2/e
Examples of Naming Carboxylic Acids
177
Tro: Chemistry: A Molecular Approach, 2/e
Practice – Name the following
178
hexanoic acid(aka caproic acid, which causes
foot odor)
2-hydroxy-3-methylbutanoic acid
Tro: Chemistry: A Molecular Approach, 2/e
Reactions of Carboxylic Acids
183
Neutralisation: Reactions with bases to form salts of the acids and water. RCOOH + NaOH RCOONa + H2O
Reactions with Reactive Metals : forming salts of the acids and H2 gas
2CH3COOH + 2Na 2CH3COONa + H2
Reactions with hydroegn carbonates: forming salts of the acids, CO2 and H2O
RCOOH + NaHCO3 RCOONa + CO2 + H2O
Reductions of Carboxylic Acids
184
Carboxylic acids are reduced by very strong reducing agents such as lithium aluminum hydride in ether, producing primary alcohols.
RCOOH LiAlH4/ether RCH2OH + H2O
Esterification
When a carboxylic acid is heated with an alcohol in the presence of concentrated sulphuric acid as catalyst, an ester is produced.
RCOOH + R′OH conc. H2SO4 RCOOR′ + H2O
Example:
CH3CH2COOH + CH3OH conc. H2SO4 CH3CH2COOCH3 + H2O propanoic acid methanol methylpropanoate
Esters R–COO–R′ Sweet odor Made by reacting carboxylic acid with an alcohol in the
presence of conc. sulphuric acid as catalyst
RCOOH + R′OH conc. H2SO4 RCOOR′ + H2O
181
Tro: Chemistry: A Molecular Approach, 2/e
Naming Esters
Carboxylic acid group always on end of main chain
• unless carboxylic acid group present C of ester group on C1
• position not indicated in name Begin name with alkyl group attached to O Name main chain with oate ending
182
Tro: Chemistry: A Molecular Approach, 2/e
Hydrolysis of Esters
Hydrolysis of esters is the reverse of esterification Acid Hydrolysis of an ester in the presence of dilute HCl or dilute
sulphuric acid produces an alcohol and a carboxylic acid If an alkali is used instead of an acid, the carboxylic acid formed will
be converted to the salt
CH3CH2COOCH3 + H2O H+/reflux CH3CH2COOH + CH3OH
methylpropanoate propanoic acid methanol
CH3CH2COOCH3 + NaOH reflux CH3CH2COONa + CH3OH
methylpropanoate sodium propanoate methanol