Progetto: Rete e-Clil
M.I.U.R. - Piano Nazionale Scuola Digitale
Capofila Rete Scuole: Liceo «G.B. Brocchi» di Bassano del Grappa (Vicenza)
Scuola della Rete:Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano delGrappa
Lavoro di «e-clil Chemistry: ALKANES» prodotto dalla:Classe 2^AT indirizzo Tecnico Agrario – a.s. 2015/2016(Bernardi Marco, Bombieri Jacopo, Cunico Davide, Feltracco Nicole, Frighetto Davide,Girardi Emanuele, Girolimetto Mattia, Lago Massimo, Maresca Ivan, Parolin Sofia,
Pasqualotto Andrea, Pertile Michelle, Reginato Denise, Terzitta Alessio, Trento Matteo,
Vignoni Nicolò, Zen Andrea, Zonta Andrea, Zurlo Giacomo)
Docenti coordinatori: Cadò Francesca, Degetto Massimo, Iess Laura
Alkanes
• General characteristics
• Nomenclature
• Physical and chemical properties
• Chemical reactions
• Carbon hybridization
• Isomerism
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
ALKANES
Alkanes are organic compounds.
They are composed of hydrogen and carbon – thatis why they are called hydrocarbons.
The atoms are joined up in a straight chain or ina ring (cycloalkanes).
CH4 (methane) is the simplest compound of thefamily of hydrocarbons.
Alkanes are saturated compounds: they arecharacterized by one carbon-to-carboncovalent single bond.
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
Alkanes are a homologous series; they have theCH2 repeating unit and their general brute formulais: CnH2n+2
ALKANES
METHANE CH4
ETHANE C2H6
PROPANE C3H8
BUTANE C4H10
PENTANE C5H12
HEXANE C6H14
HEPTANE C7H16
OCTANE C8H18
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
SOURCES AND INDUSTRIAL USES
The main sources of alkanes are:
• Natural gas
• Oil
Hydrocarbon compounds can contain from 1 to 30-40 carbon atoms.
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
NATURAL GASES
Natural gas contains only the mostvolatile alkanes, i.e. those with alower molecular weight.
It is mainly composed of methaneand a small quantity of ethane,propane and butane.
GPL
Propane and butane are used asfuels at a liquid state, and aremarketed in pressure cylinders withthe GPL acronym (liquefiedpetroleum gas).
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
OIL
Crude oil is a mixture of solid, liquid, gaseoushydrocarbons, which also contains small quantitiesof organic compounds.
In the mixture there are:
• alkanes
• cycloalkanes
• aromatic hydrocarbons
• rare alkenes
• no alkynes
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
NOMENCLATUREThe IUPAC nomenclature is the result of a series of rules:
Nr C Atoms Root name
1 Meth-
2 Eth-
3 Prop-
4 But-
5 Pent-
6 Hex-
7 Hept-
8 Oct-
10 carbon atoms: Dec-ane
Example:
1) find the longest chain of carbon atoms
2) build the name combining the root (= number of carbon atoms in the main chain; table on the left below) with suffix «-ane».
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
3) Use locator number to indicate the carbon atoms of the main chain:the numbering of carbon starts from the carbon closest to the firstbranch.
123
456
78910
4) It gives its name to the substituents or alkyl radicals(Hydrocarbon fragments obtained by removing an H group from thecompound: the name is obtained from the corresponding alkane byreplacing –ane with –yle.) Example:From alkane: CH4 is «methane» and the radical is –CH3 «methyle»From alkane: CH3-CH3 is «ethane» and the radical is –CH2-CH3 «ethyle»
5) Use the locator number to indicate the position of substituents(separated by a hyphen) along the main chain:
3-methyle; 4-methyle; 4-ethyle; 5-methyle; 6-methyle; 6-ethyle
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
6) Mention in alphabetical order the alkyls or substituents. If there aresubstituents that are repeated, group the position numbers andindicate with a prefix (di-, tri-, tetra-, penta-, hexa-...) the amount ofsubstituents of that type. If the substituents end in «-yle», eliminatethe final «e».
3-methyle
4-methyle
4-ethyle
5-methyle
6-methyle
6-ethyle
3,4,5,6-tetra-methyl
4,6-di-ethyl
4,6-diethyl-3,4,5,6-tetramethyl
Alphabetical order
There are 4 «methyl» substituents
There are 2 «ethyl» substituents
7) Assemble the full name before indicating the substituents followed bythe name of the main chain.
4,6-diethyl-3,4,5,6-tetramethyl-decane
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
PHYSICAL AND CHEMICAL PROPERTIES OF ALKANES
AND CYCLOALKANES
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
Physical status:
A lot of physical and chemical properties of alkanesdepend on the complexity of their molecules, namelyon the length of the main chain of carbon atoms andon its lateral branching.
• alkanes with 1,2,3 and 4 carbon atoms are aeriform
• alkanes with 5-17 carbon atoms are liquid• alkanes with 18 or more carbon atoms are solid
Density:
• increases with the length and the branching• in general, all alkanes have a lower density than
water and for this reason they float on water.
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
Melting and boiling pointsas for alkanes with 5 or more carbon atoms, eachextra carbon atom increases the temperature by20-30 °C.As their branching increases, the temperaturedecreases.
The properties can greatly vary according tothe type of structural isomerism (substanceswith the same brute formula, but with a differentarrangement of atoms).
SolubilityAlkanes are insoluble in water (hydrophobic) and inthe polar solvents, while they are soluble in non-polar solvents (benzene, ether, chloroform, carbontetrachloride).
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
ReactivityIn general, alkanes are compounds relativelyunreactive and rather stable (for this reason theywere called paraffines – from Latin par (um)barely + aff (īnis) connected + -in)
Their excellent stability is due to:
• the pure covalent bonds among carbon atoms,where the e- pair of the sigma bond is locatedand equally shared between two atoms;
• the C-H bonds have a low-polarity (the electro-negativity difference is low, around 0,24), whosepolarizing effects are reduced thanks to thesymmetric disposition of hydrogen atoms aroundthe carbon atoms, thus greatly increasing themolecule stability.
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
the simple C-C covalent bonds allow the carbonatoms to rotate around their bond in the open-chainmolecules. In this way, molecules, which are limitedby the repulsion of the same sign charges, may havedifferent structures (V.S.E.P.R. theory)
under standard conditions, alkanes do not react withbases, acids and oxidizing agents
alkanes can react with high temperature, ultravioletlight (UV) or in the presence of catalysts. The fewpossible reactions for alkanes are:
• Radical substitution (substitution of H for other elements, inparticular halogens → radical halogenation reaction)
• Combustion (oxidation reaction)
• Thermal and catalytic cracking (breaking of C-C and C-Hbonds)
• Halogenation
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
ALKANE REACTIONS
COMBUSTION (oxidation reaction)
HALOGENATION
RADICAL SUBTITUTION REACTIONS(thermal and/or catalytic cracking)
NUCLEOPHILIC SUBSTITUTION REACTIONS
ELETROPHILIC SUBSTITUTION REACTIONS
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
COMBUSTIONCombustion is the most common reaction. Hydrocarbonsburn in contact with air, producing carbon dioxide (CO2),water (H2O) and developing a huge quantity of heat,which is the main product of the oxidation reaction.
Representation of the methane reaction:
CH4+2O2 → CO2+2H2O+HEAT
In an airless environment, in addition to carbon dioxide (CO2),carbon monoxide (CO) may also be produced, which creates avery toxic environment.
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
HALOGENATIONAlkanes are the least reactive class of organic compoundsbecause they are made up of atoms characterized by verystrong, non-polar bonds.
CH4 + Cl2 → CH3Cl + HCl
CH3Cl + Cl2 → CH2Cl2 + HCl
CH2Cl2 + Cl2 → CHCl3 + HCl
CHCl3 + Cl2 → CCl4 + HCl
To obtain monohalogenatedcompounds it is necessaryto work in an excess ofalkane; to obtain a poli-halogenated compound it isnecessary to work in anexcess of halogen.
They can react with halogens F2 , Cl2 and Br2 (exothermic
reactions) thanks to:
Heat
Irradiation with visible or UV light
If there is an excess of halogens, the substitution reaction
continues, giving rise to a mixture of poly-halogenated
compounds
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
RADICAL SUBSTITUTIONThe radical substitution is divided into three stages:
Initiation: the reaction is started by the homolytic
cleavage (cracking) of X2 (x = any element) by heat or
by providing a quantum of energy (hn).
Propagation: the resulting radical reacts with the alkane
producing an alkyl radical, which, in turn, reacts with a
molecule of halogen, thus forming the alkyl halide and a
halogen radical.
Termination: when the resulting radicals recombine, the
reaction terminates.
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
Example:
Initiation (formation of a halogen radical by cracking):
Cl−Cl Cl● + Cl●T / hn
Propagation
Termination
Cl● + Cl● Cl−Cl
+ →
Alkyl halide
Alkyl radical
Halogenradicals
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
NUCLEOPHILIC AND ELECTROPHILIC
• Nucleophilic reagents are the electron-donors, i.e.:
negative ions
the groups of atoms having unshared electron pairs.
Nucleophilic reagents react with the site of a chemicalspecies in which there is an atom lacking electrons(electrophilic site).
• Electrophilic reagents are the electron-acceptors, i.e.:
positive ions (H+, H3O+, NO2
+; R+, carbocation)
atomic groups lacking electrons (AlCl3, BF3).
They react with atoms rich in electrons (nucleophilic site).
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
NUCLEOPHILIC SUBSTITUTION
The nucleophilic substitution is a substitution reaction in
which a nucleophile replaces, in a molecule, another
nucleophilic group, which takes the name of the leaving
group.
Leaving group= atom or group of atoms which breaks
away from a chemical substance leaving a residue or the
main part. This leaving group departs, with a pair of
electrons in heterolytic bond cleavage, as stable group.
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
ELECTROPHILIC SUBSTITUTION
The electrophilic substitution is a chemical reactionin which an electrophile replaces another group (ora simple hydrogen atom) in a molecule
ELECTROPHILE SITE
NUCLEOPHILIC REAGENT
NUCLEOPHILIC LEAVING GROUP
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
CARBON HYBRIDIZATIONThe presence of one S orbital and three P orbitals in thesecond energetic level (valence level) allows the carbon to
combine the S orbital with theP orbital, thus getting sp1,sp2, sp³ hybrid orbitals,according to the number of Porbitals involved.
The sp³ hybrid orbital allowsthe molecule to direct thebonds in space arranging theatoms at the maximumdistance so as to minimizetheir repulsion (V.S.E.P.R.theory)
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
CHARACTERISTICS OF SIGMA BOND
The carbon atoms link up to form simple covalentbonds of σ (sigma) type: they are bonds that allow theatoms to rotate around the axis defined by the bondplane.
σ bondRotation
sp orbital
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
ISOMERISM
ISOMERISMSame brute formula but
different physical properties
can be:
STEREOISOMERISMdifferent atom
arrangement in space
STRUCTURAL OR CONSTITUTIONAL ISOMERS
Different sequences of atoms or groups of atoms in the molecules
subdivided into:
CHAIN ISOMERSsame number of carbon atoms
arranged in a different way
POSITION ISOMERSsame chain but different
position ofsubstituent atoms or
functional groups
FUNCTIONAL ISOMERSthe different atom
arrangement determines different functional
groups
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
STEREOISOMERISM
Stereoisomers are compounds whichpresent the same sequence ofmutually bonded atoms but differ inthe spatial orientation of theircomponent atoms.
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
Stereoisomerism is divided into:
Configurational
isomers:different arrangement of the
molecular components
Conformational
isomers:produce a rotation or a grouping of atoms around a C-C central simple
bond
Enantiomers(Optical isomers)
Diastereomers(Geometrical isomers)
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
Enantiomers and chiralityEnantiomers are molecular entities that are non-superimposable mirror images of each other.
Chirality is a property of enantiomerism.
To understand molecular chirality it is advisable touse molecular models.
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
It is found in organic molecules and is related to the tetrahedral form of the
C atom bonds.
The carbon atom becomes a chiral when it is bonded to four atoms or
groups of different atoms.
The chiral carbon atom is calledstereocenter.
Chirality
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
Diastereomers
A diastereomer is a stereoisomer which differs from an enantiomer.
Stereisomers that are not mirror images:
1-2, 3-4 pairs of enantiomers
1-4, 1-3, 2-3, 2-4 pairs of distereoisomers
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
Conformational isomerism
In Alkanes carbon atoms, having sp3 hybridization,can get a tetrahedral spatial configuration and themolecules are fairly free to move, namely to rotatearound C-C pure covalent bonds.
Therefore, elements can have different arrangementsin space, namely a different conformationalisomerism.
Isomers do not have thesame stability: the moleculeatoms tend to move inspace towards the 3D lessenergetic and more stableform.
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
Conformational Isomers
Owing to a free rotation around asimple C-C bond, they can havedifferent conformations. This rotationgives rise to an infinite number ofstructures called Conformers orRotamers.
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
The most important conformations are «the chair» and«the boat»: they are in equilibrium with each other so asto lean towards the conformation which is more stable.
Chair conformation
Boat conformation
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
In conformations, the hydrogen atoms can place themselves,in relation to the carbon atom ring, as follows:
• as axial substituents (hydrogen atoms perpendicular to theplane defined by carbon atoms – in red in the picture)
• as equatorials substituents (hydrogens on the same planedefined by carbon atoms – in blue in the picture).
Example of two chair conformations in the limit equilibriumbetween the space positions taken by the atoms.
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
GEOMETRIC ISOMERISM
dimethylcyclohexane dimethylcyclohexane
Geometric isomerism can be present inalkanes and cycloalkanes.The two pictures below show the differentposition of the two methyl groups:
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
Substituentson the same side of the plane
They are called ‘CIS’ if the two substituents (CH3) are on the same side of the ring plane.
dimethylcyclohexane
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
Substituentson opposite sides of the plane
They are called ‘TRANS’ if the two substituents are on opposite sides of the ring plane.
dimethylcyclohexane
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
STRUCTURAL ISOMERISM
It represents the differentsequence of atoms or groups of
atoms in the molecule.Structural isomerism can be:
CHAIN POSITION FUNCTIONAL
ISOMERISM ISOMERISM ISOMERISM
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
CHAIN ISOMERISM
Same number of carbon atoms (C4) but different chain structure
CH3-CH2-CH2-CH3
CH3-CH-CH3
CH3
CH2-CH2
CH2-CH2
Linear isomerism
Branchedisomerism
Cyclicisomerism
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
CHAIN ISOMERISM concerns the structure of the carbon skeleton,
namely the presence and positionof the branching or rings.
cyclobutene
Trimethyl-2-pentene ethylcyclohexane
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
POSITION ISOMERISMSame number of carbon atoms
(C4) but different position
POSITION ISOMERISM POSITION ISOMERISM
with ONE SUBSTITUENT with DOUBLE BONDS
CH2-CH2-CH3
|NH2
CH3-CH-CH3
|NH2
CH2=CH-CH2-CH3
CH3-CH=CH-CH3
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
POSITION ISOMERISM concerns the position ofmultiple bonds or groups containg atomsdifferent from carbon and hydrogen: ortho- (o),meta- (m), para- (p) position.
O-xilene m-xilene p-xilene
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16
FUNCTION ISOMERISM
Isomers with the same brute formula, but withdifferent «functional groups».Example: C4H10O
CH3-CH2-CH2-CH2-OH alcohol
CH3-CH2-O-CH2-CH3 ether
Classe 2AT Indirizzo Tecnico Agrario – Istituto Statale di Istruzione Superiore «A. Parolini» di Bassano del Grappa – a.s. 2015/16