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1-1-11
Organic Organic ChemistryChemistry
William H. BrownWilliam H. BrownChristopher S. FooteChristopher S. FooteBrent L. IversonBrent L. Iverson
1-1-22
Covalent Covalent Bonding & Bonding & Shapes of Shapes of MoleculesMolecules
Chapter 1Chapter 1
1-1-33
Organic ChemistryOrganic Chemistry The study of the compounds of carbon Over 10 million compounds have been identified• about 1000 new ones are identified each day!
C is a small atom • it forms single, double, and triple bonds• it is intermediate in electronegativity (2.5)• it forms strong bonds with C, H, O, N, and some metals
1-1-44
Schematic View of an AtomSchematic View of an Atom• a small dense nucleus,
diameter 10-14 - 10-15 m, which contains positively charged protons and most of the mass of the atom
• an extranuclear space, diameter 10-10 m, which contains negatively charged electrons
1-1-55
Electron Configuration of AtomsElectron Configuration of Atoms Electrons are confined to regions of space called
principle energy levels (shells)• each shell can hold 2n2 electrons (n = 1,2,3,4......)
Shell
Number of Electrons Shell
Can Hold
Relative Energiesof Electrons
in These Shells3218 8 2
4321
higher
lower
1-1-66
Electron Configuration of AtomsElectron Configuration of Atoms Shells are divided into subshells called orbitals,
which are designated by the letters s, p, d, f,........• s (one per shell) • p (set of three per shell 2 and higher) • d (set of five per shell 3 and higher) .....
Shell Orbitals Contained in That Shell321 1s
2s, 2px, 2py, 2pz
3s, 3px, 3py, 3pz, plus five 3d orbitals
1-1-77
Electron Configuration of AtomsElectron Configuration of Atoms Aufbau Principle:Aufbau Principle: • orbitals fill in order of increasing energy from lowest
energy to highest energy Pauli Exclusion Principle:Pauli Exclusion Principle: • only two electrons can occupy an orbital and their
spins must be paired Hund’s Rule:Hund’s Rule: • when orbitals of equal energy are available but there
are not enough electrons to fill all of them, one electron is added to each orbital before a second electron is added to any one of them
1-1-88
Electron Configuration of AtomsElectron Configuration of Atoms The pairing of electron spins
1-1-99
Electron Configuration of AtomsElectron Configuration of Atoms Table 1.3 The Ground-State Electron
Configuration of Elements 1-18
1-1-1010
Lewis Dot StructuresLewis Dot Structures Gilbert N. Lewis Valence shell:Valence shell: • the outermost occupied electron shell of an atom
Valence electrons:Valence electrons: • electrons in the valence shell of an atom; these
electrons are used to form chemical bonds and in chemical reactions
Lewis dot structure:Lewis dot structure: • the symbol of an element represents the nucleus and
all inner shell electrons• dots represent valence electrons
1-1-1111
Lewis Dot StructuresLewis Dot Structures Table 1.4 Lewis Dot Structures for Elements 1-18
N OB
H
Li Be
Na
He
Cl
F
S
Ne
Ar
C
SiAl P
1A 2A 3A 4A 5A 6A 7A 8A
Mg :
:::::
.
.
.
.
.
.
.
..
. .
. .
..
.
:
:
:
::::::::
::::::.
:::
:
1-1-1212
Lewis Model of BondingLewis Model of Bonding Atoms bond together so that each atom acquires
an electron configuration the same as that of the noble gas nearest it in atomic number• an atom that gains electrons becomes an anionanion• an atom that loses electrons becomes a cationcation• the attraction of anions and cations leads to the
formation of ionic solidsionic solids• an atom may share electrons with one or more atoms
to complete its valence shell; a chemical bond formed by sharing electrons is called a covalent bondcovalent bond
• bonds may be partially ionic or partially covalent; these bonds are called polar covalent bondspolar covalent bonds
1-1-1313
ElectronegativityElectronegativity Electronegativity:Electronegativity: • a measure of an atom’s attraction for the electrons it
shares with another atom in a chemical bond Pauling scalePauling scale• generally increases left to right in a row• generally increases bottom to top in a column
1-1-1414
Formation of IonsFormation of Ions A rough guideline: • ions will form if the difference in electronegativity
between interacting atoms is 1.9 or greater• example: sodium (EN 0.9) and fluorine (EN 4.0)• we use a single-headed (barbed) curved arrow to show
the transfer of one electron from Na to F
• in forming Na+F-, the single 3s electron from Na is transferred to the partially filled valence shell of F
Na + F Na+ F -••••••
••
••••
••
+ F-(1s22s22p6)Na+(1s22s22p6)F(1s22s22p5)+Na(1s22s22p63s1)
1-1-1515
Covalent BondsCovalent Bonds The simplest covalent bond is that in H2
• the single electrons from each atom combine to form an electron pair
• the shared pair functions in two ways simultaneously; it is shared by the two atoms and fills the valence shell of each atom
The number of shared pairs• one shared pair forms a single bond• two shared pairs form a double bond• three shared pairs form a triple bond
H H H-H+ • ΔH0 = -435 kJ (-104 kcal)/m ol•
1-1-1616
Polar and Nonpolar Covalent BondsPolar and Nonpolar Covalent Bonds Although all covalent bonds involve sharing of
electrons, they differ widely in the degree of sharing
We divide covalent bonds into• nonpolar covalent bonds• polar covalent bonds
Difference in ElectronegativityBetween Bonded Atoms Type of BondLess than 0.50.5 to 1.9Greater than 1.9
Nonpolar covalentPolar covalentIons form
1-1-1717
Polar and Nonpolar Covalent BondsPolar and Nonpolar Covalent Bonds• an example of a polar covalent bond is that of H-Cl• the difference in electronegativity between Cl and H is
3.0 - 2.1 = 0.9• we show polarity by using the symbols ++ and --, or by
using an arrow with the arrowhead pointing toward the negative end and a plus sign on the tail of the arrow at the positive end
H Cl+ δ-
H Cl
1-1-1818
Polar Covalent BondsPolar Covalent Bonds Bond dipole moment (Bond dipole moment (mm):): • a measure of the polarity of a covalent bond• the product of the charge on either atom of a polar
bond times the distance between the nuclei• Table 1.7 shows average bond dipole moments of
selected covalent bonds
H-OH-NH-C
H-S C-I
C-FC-ClC-Br C-N
-
C-O
C=N
C=O
-
Bond Dipole (D) Bond
1.4
1.51.51.41.2
Bond
Bond Dipole (D)
1.30.3 0.7
0.20.7
2.3
3.5
Bond Dipole (D)Bond
1-1-1919
Lewis StructuresLewis Structures To write a Lewis structure• determine the number of valence electrons• determine the arrangement of atoms• connect the atoms by single bonds• arrange the remaining electrons so that each atom has
a complete valence shell• show a bonding pair of electrons as a single line• show a nonbonding pair of electrons as a pair of dots• in a single bond atoms share one pair of electrons, in a
double bond they share two pairs of electrons, and in a triple bond they share three pairs of electrons
1-1-2020
Lewis Structures - Table 1.3Lewis Structures - Table 1.3
In neutral molecules• hydrogen has one bond• carbon has 4 bonds and no lone pairs• nitrogen has 3 bonds and 1 lone pair• oxygen has 2 bonds and 2 lone pairs• halogens have 1 bond and 3 lone pairs
H2O (8) NH3 (8) CH4 (8) HCl (8)
C2H4 (12) C2H2 (10) CH2O (12) H2CO3 (24)
H-O-H H-N-HH
H-C-HH
HH-Cl
H-C C-HH
HC O
H
HC C
H
H O OCH HO
Ethylene
Hydrogen chlorideMethaneAmmoniaWater
Carbonic acidFormaldehydeAcetylene
1-1-2121
Formal ChargeFormal Charge Formal charge:Formal charge: the charge on an atom in a
molecule or a polyatomic ion To derive formal charge
1. write a correct Lewis structure for the molecule or ion2. assign each atom all its unshared (nonbonding)
electrons and one-half its shared (bonding) electrons3. compare this number with the number of valence
electrons in the neutral, unbonded atom
Number of valence electrons in the neutral, unbonded atom
All unsharedelectrons
One half of all shared electrons
+Formalcharge
=
1-1-2222
Formal ChargeFormal Charge Example:Example: Draw Lewis structures, and show which atom in
each bears the formal chargeNH2
- HCO3- CO3
2-
CH3NH3+ HCOO- CH3COO-
(b) (c)
(d) (e) (f)
(a)
1-1-2323
Exceptions to the Octet RuleExceptions to the Octet Rule Molecules containing atoms of Group 3A
elements, particularly boron and aluminum
Aluminum chloride
:::
F B
F
F
Cl Al
Cl
Cl
6 electrons in the valence shells of boron
and aluminum
Boron trifluoride: :
: :
: :
::
::
:
::
::
1-1-2424
Exceptions to the Octet RuleExceptions to the Octet Rule Atoms of third-period elements have 3d orbitals
and may expand their valence shells to contain more than 8 electrons• phosphorus may have up to 10
::
Phosphorus pentachloride
Phosphoricacid
P
ClCl Cl
Cl ClCH3-P-CH3
CH3Trimethyl-phosphine
H-O-P-O-HO
O-H
:
:
:
::
::
::
::::
::
:
:
::
:
:
1-1-2525
Exceptions to the Octet RuleExceptions to the Octet Rule• sulfur, another third-period element, forms
compounds in which its valence shell contains 8, 10, or 12 electrons
:::H-S-H CH3-S-CH3 H-O-S-O-H
O
OO
Sulfuricacid
Hydrogensulfide
Dimethylsulfoxide
::
::
: : : :
: :
1-1-2626
Functional GroupsFunctional Groups Functional group:Functional group: an atom or group of atoms
within a molecule that shows a characteristic set of physical and chemical properties
Functional groups are important for three reason; they are1. the units by which we divide organic compounds into
classes2. the sites of characteristic chemical reactions3. the basis for naming organic compounds
1-1-2727
AlcoholsAlcohols contain an -OH (hydroxylhydroxyl) group
Ethanol may also be written as a condensed condensed structural formulastructural formula
H-C-C-O-HH
H
H
H::-C-O-H
Ethanol(an alcohol)
Functionalgroup
CH3-CH2-OH CH3CH2OHor
1-1-2828
AlcoholsAlcohols• alcohols are classified as primary (1°), secondary (2°),
or tertiary (3°) depending on the number of carbon atoms bonded to the carbon bearing the -OH group
CH3-C-OHCH3
CH3CH3-C-OH
CH3
H
CH3
CH3CH3-C-OH
A 1° alcohol A 2° alcohol A 3° alcohol
1-1-2929
AlcoholsAlcohols• there are two alcohols with molecular formula C3H8O
CH3CH2CH2OH
CH3CHCH3
OH
H-C-C-C-O-HH
H
H
H
H
H
C-C-C-HH
HOH
HHH
H
or
ora 2° alcohol
a 1° alcohol
1-1-3030
AminesAmines contain an amino groupamino group; an sp3-hybridized
nitrogen bonded to one, two, or three carbon atoms• an amine may by 1°, 2°, or 3°
CH3 N HH
CH3 N HCH3
CH3 N CH3CH3
Methylamine(a 1° amine)
Dimethylamine(a 2° amine)
Trimethylamine(a 3° amine)
: : :
1-1-3131
Aldehydes and KetonesAldehydes and Ketones contain a carbonyl (C=O) groupcarbonyl (C=O) group
C HO
CH3-C-HO
CH3-C-CH3
OCO
Functionalgroup
Acetaldehyde(an aldehyde)
Acetone(a ketone)
Functionalgroup
1-1-3232
Carboxylic AcidsCarboxylic Acids contain a carboxyl (-COOH) groupcarboxyl (-COOH) group
C OO
H CH3-C-O-HO
CH3COOH CH3CO2H: ::
: or orAcetic acid
(a carboxylic acid)Functional
group
1-1-3333
Carboxylic EstersCarboxylic Esters Ester:Ester: a derivative of a carboxylic acid in which
the carboxyl hydrogen is replaced by a carbon group
C OO
Functionalgroup
CH3-C-O-CH2-CH3
Ethyl acetate(an ester)
::
: :O
1-1-3434
Carboxylic AmideCarboxylic Amide Carboxylic amidearboxylic amide, commonly referred to as an
amideamide: a derivative of a carboxylic acid in which the -OH of the -COOH group is replaced by an amine
• the six atoms of the amide functional group lie in a plane with bond angles of approximately 120°
CH3-C-N-HH
Acetamide(a 1° amide)
OC NO
Functionalgroup
1-1-3535
VSEPRVSEPR Based on the twin concepts that• atoms are surrounded by regions of electron density• regions of electron density repel each other
HC C
H
O C
CH
NH
HC
HHO
H
CH C H
H
O
4 regions of e- density(tetrahedral, 109.5°)
3 regions of e- density(trigonal planar, 120°)
2 regions of e- density(linear, 180°)
H
CH H
HN
H HH
:
::
::
::
:
H HO
CH N
1-1-3636
VSEPR ModelVSEPR Model Example:Example: predict all bond angles for these molecules and
ions(a) NH4
+ (b) CH3NH2
(f) H2CO3 (g) HCO3-(e) CH3CH=CH2
(i) CH3COOH(h) CH3CHO
(d) CH3OH
(j) BF4-
1-1-3737
Polar and Nonpolar MoleculesPolar and Nonpolar Molecules To determine if a molecule is polar, we need to
determine • if the molecule has polar bonds• the arrangement of these bonds in space
Molecular dipole moment (Molecular dipole moment (mm):): the vector sum of the individual bond dipole moments in a molecule• reported in debyes (D)
1-1-3838
Polar and Nonpolar MoleculesPolar and Nonpolar Molecules these molecules have polar bonds, but each has
a zero dipole moment
O C O
Carbon dioxidem = 0 Δ
B
F
F
F
Boron trifluoriem = 0 Δ
C
Cl
ClClCl
Carbon tetrachloriem = 0 Δ
1-1-3939
Polar and Nonpolar MoleculesPolar and Nonpolar Molecules these molecules have polar bonds and are polar
moleculesN
HH
HO
H H
Waterm = 1.85Δ
Am m onia m = 1.47Δ
irectionof ipolem om ent
irectionof ipolem om ent
1-1-4040
Polar and Nonpolar MoleculesPolar and Nonpolar Molecules• formaldehyde has polar bonds and is a polar molecule
Formaldehyde m = 2.33 Δ
irectionof ipolem om ent H HC
O
1-1-4141
ResonanceResonance For many molecules and ions, no single Lewis
structure provides a truly accurate representation
Ethanoate ion(acetate ion)
CO
OH3CC
O
OH3C
-
-
and
1-1-4242
ResonanceResonance Linus Pauling - 1930s• many molecules and ions are best described by
writing two or more Lewis structures• individual Lewis structures are called contributing
structures• connect individual contributing structures by double-
headed (resonance) arrows• the molecule or ion is a hybrid of the various
contributing structures
1-1-4343
ResonanceResonance Examples:Examples: equivalent contributing structuresequivalent contributing structures
Acetate ion(equivalent contributing
structures)
Nitrite ion(equivalent contributing
structures)
:
:
:
:: : :
NO -
O: N
O
O -:
: : :
:
:
: :
: :C
O -
OCH3 C
O
O -CH3
: :
::
1-1-4444
ResonanceResonance Curved arrow:Curved arrow: a symbol used to show the
redistribution of valence electrons In using curved arrows, there are only two
allowed types of electron redistribution:• from a bond to an adjacent atom• from an atom to an adjacent bond
Electron pushing is a survival skill in organic chemistry• learn it well!
1-1-4545
ResonanceResonance All contributing structures must1. have the same number of valence electrons2. obey the rules of covalent bonding• no more than 2 electrons in the valence shell of H • no more than 8 electrons in the valence shell of a 2nd
period element• 3rd period elements, such as P and S, may have up to
12 electrons in their valence shells3. differ only in distribution of valence electrons; the
position of all nuclei must be the same4. have the same number of paired and unpaired electrons
1-1-4646
ResonanceResonance The carbonate ion, for example• a hybrid of three equivalent contributing structures• the negative charge is distributed equally among the
three oxygens
1-1-4747
ResonanceResonance Preference 1:Preference 1: filled valence shells• structures in which all atoms have filled valence shells
contribute more than those with one or more unfilled valence shells
••••••
Greater contribution; both carbon and oxygen have complete valence shells
Lesser contribution;carbon has only 6 electrons in its valence shell
+ +CCH3 OCH3 O
H
HC
H
H
1-1-4848
ResonanceResonance Preference 2:Preference 2: maximum number of covalent
bonds• structures with a greater number of covalent bonds
contribute more than those with fewer covalent bonds
••
••••
Greater contribution(8 covalent bonds)
Lesser contribution(7 covalent bonds)
+ +CCH3 OCH3 O
H
HC
H
H
1-1-4949
ResonanceResonance Preference 3:Preference 3: least separation of unlike charge• structures with separation of unlike charges contribute
less than those with no charge separation
Lesser contribution(separation of unlike
charges)
CH3-C-CH3 CH3-C-CH3
Greater contribution(no separation of unlike charges)
O -O
::
:::
1-1-5050
ResonanceResonance Preference 4:Preference 4: negative charge on the more
electronegative atom • structures that carry a negative charge on the more
electronegative atom contribute more than those with the negative charge on the less electronegative atom
CH3CH3H3CCH3H3CCO
CO
H3CC
O
(b)Greater
contribution
(c)Should notbe drawn
(a)Lesser
contribution
(1) (2)
1-1-5151
Quantum or Wave MechanicsQuantum or Wave Mechanics Albert Einstein: E = hn (energy is quantized)• light has particle properties
Louis deBroglie: wave/particle duality
Erwin Schrödinger: wave equation• wave function, wave function, : a solution to a set of equations that
depicts the energy of an electron in an atom• each wave function is associated with a unique set of
quantum numbers• each wave function occupies three-dimensional space
and is called an orbitalorbital• 22 is the probability of finding an electron at a given
point in space
l = hmν
1-1-5252
Shapes of 1Shapes of 1ss and 2 and 2ss Orbitals Orbitals Probability distribution (2) for 1s and 2s orbitals
showing an arbitrary boundary surface containing about 95% of the electron density
1-1-5353
Shapes of a Set of 2Shapes of a Set of 2pp Atomic Orbitals Atomic Orbitals Three-dimensional shapes of 2p atomic orbitals
1-1-5454
Molecular Orbital TheoryMolecular Orbital Theory Electrons in atoms exist in atomic orbitals Electrons in molecules exist in molecular orbitals
(MOs) Using the Schrödinger equation, we can
calculate the shapes and energies of MOs
1-1-5555
Molecular Orbital TheoryMolecular Orbital Theory Rules:• combination of n atomic orbitals (mathematically
adding and subtracting wave functions) gives n MOs (new wave functions)
• MOs are arranged in order of increasing energy• MO filling is governed by the same rules as for atomic
orbitals:• Aufbau principle: fill beginning with LUMO• Pauli exclusion principle: no more than 2e- in a MO• Hund’s rule: when two or more MOs of equivalent
energy are available, add 1e- to each before filling any one of them with 2e-
1-1-5656
Molecular Orbital TheoryMolecular Orbital Theory Terminology• ground state = lowest energy state• excited state = NOT lowest energy state• = sigma bonding MO• * = sigma antibonding MO• p = pi bonding MO• p* = pi antibonding MO• HOMO = highest occupied MO• LUMO = lowest unoccupied MO
1-1-5757
Molecular Orbital TheoryMolecular Orbital Theory Sigma 1s bonding and antibonding MOs
1-1-5858
Molecular Orbital TheoryMolecular Orbital Theory• MO energy diagram for H2: (a) ground state and (b)
lowest excited state
1-1-5959
Molecular OrbitalsMolecular Orbitals• computed sigma bonding and antibonding MOs for H2
1-1-6060
Molecular OrbitalsMolecular Orbitals pi bonding and antibonding MOs
1-1-6161
Molecular OrbitalsMolecular Orbitals• computed pi bonding and antibonding MOs for
ethylene
1-1-6262
Molecular OrbitalsMolecular Orbitals• computed pi bonding and antibonding orbitals for
formaldehyde
1-1-6363
Hybrid OrbitalsHybrid Orbitals The Problem:• bonding by 2s and 2p atomic orbitals would give bond
angles of approximately 90°• instead we observe bond angles of approximately
109.5°, 120°, and 180° A Solution• hybridization of atomic orbitals• 2nd row elements use sp3, sp2, and sp hybrid orbitals
for bonding
1-1-6464
Hybrid OrbitalsHybrid Orbitals Hybridization of orbitals (L. Pauling)• the combination of two or more atomic orbitals forms
a new set of atomic orbitals, called hybrid orbitals We deal with three types of hybrid orbitals
spsp33 (one s orbital + three p orbitals)spsp22 (one s orbital + two p orbitals)spsp (one s orbital + one p orbital)
Overlap of hybrid orbitals can form two types of bonds depending on the geometry of overlap bondsbonds are formed by “direct” overlappp bondsbonds are formed by “parallel” overlap
1-1-6565
spsp33 Hybrid Orbitals Hybrid Orbitals• each sp3 hybrid orbital
has two lobes of unequal size
• the sign of the wave function is positive in one lobe, negative in the other, and zero at the nucleus
• the four sp3 hybrid orbitals are directed toward the corners of a regular tetrahedron at angles of 109.5°
1-1-6666
spsp33 Hybrid Orbitals Hybrid Orbitals• orbital overlap pictures of methane, ammonia, and
water
1-1-6767
spsp22 Hybrid Orbitals Hybrid Orbitals• the axes of the three sp2 hybrid orbitals lie in a plane
and are directed toward the corners of an equilateral triangle
• the unhybridized 2p orbital lies perpendicular to the plane of the three hybrid orbitals
1-1-6868
Bonding in EthyleneBonding in Ethylene
1-1-6969
Bonding in FormaldehydeBonding in Formaldehyde
1-1-7070
spsp Hybrid Orbitals Hybrid Orbitals• two lobes of unequal size at an angle of 180°• the unhybridized 2p orbitals are perpendicular to each
other and to the line created by the axes of the two sp hybrid orbitals
1-1-7171
Bonding in Acetylene, CBonding in Acetylene, C22HH22
1-1-7272
Hybrid OrbitalsHybrid Orbitals
H-C-C-HH
H
H
H
H-C C-H
C CH
HH
H
OrbitalHybrid-ization
Types of Bonds
to Carbon Example
sp3 4 sigma bonds
sp2 3 sigma bondsand 1 pi bond
sp 2 sigma bondsand 2 pi bonds
Ethane
Ethylene
Acetylene
Name
PredictedBond
Angles
109.5°
120°
180°
GroupsBonded
to Carbon
4
2
2
1-1-7373
Bond Lengths and Bond StrengthsBond Lengths and Bond Strengths
H-C-C-HH
H
H
H
HC C
H
H H
H-C C-H
C-C
C-C
C-C
C-H
C-H
C-H
Formula BondOrbitalOverlap
Bond Length(pm)
Bond Strength[kJ (kcal)/mol]
sp3-sp3
sp2-1s
sp-sp, two 2p-2psp-1s
sp3-1s
sp2-sp2, 2p-2p
153.2111.4
133.9110.0
121.2109.0
376 (90)422 (101)
727 (174)464(111)
966 (231)556 (133)
Ethane
Ethylene
Acetylene
Name
1-1-7474
Covalent Covalent Bonds & Bonds & Shapes of Shapes of MoleculesMolecules
End Chapter 1End Chapter 1