hapter 24 From Petroleum to Pharmaceuticals 24.1 Petroleum Refining and the ydrocarbons 24.2 Functional Groups and Organic Synthesis 24.3 Pesticides and Pharmaceuticals IR Tutor and Infrared Spectroscopy
ydrocarbons Aliphatic Aromatic
ydrocarbons Aliphatic Aromatic Alkanes Alkenes Alkynes
ydrocarbons Aliphatic Alkanes are hydrocarbons in which all of the bonds are single bonds. Alkanes
ydrocarbons Aliphatic Alkenes are hydrocarbons that contain at least one carbon-carbon double bond. Alkenes
ydrocarbons Aliphatic Alkynes are hydrocarbons that contain a carbon- carbon triple bond. Alkynes
ydrocarbons The most common aromatic hydrocarbons are those that contain a benzene ring. Aromatic
Reactive Sites in ydrocarbons The Functional Group oncept
Functional Group a structural unit in a molecule responsible for its characteristic chemical behavior and its IR spectroscopic characteristics
Alkanes R R X functional group is a hydrogen atom the reaction that takes place is termed a substitution one of the hydrogens is substituted by some other atom or group, X
R Alkanes functional group is a hydrogen R X the reaction that takes place is substitution one of the hydrogens is substituted by some other atom or group + l 2 l + l
Functional Groups in ydrocarbons alkanes R alkenes R, double bond alkynes R, triple bond aromatics Ar,, double bond
Some Key Functional Groups
Families of organic compounds and their functional groups Alcohols RO Alkyl halides RX (X = F, l,, Br, I) Amines primary amine: RN 2 secondary amine: R 2 N tertiary amine: R 3 N Ethers ROR
Many classes of organic compounds contain a carbonyl group O R O arbonyl group Acyl group
Many classes of organic compounds contain a carbonyl group O O R arbonyl group Aldehyde
Many classes of organic compounds contain a carbonyl group O O R R' arbonyl group Ketone
Many classes of organic compounds contain a carbonyl group O O R O arbonyl group arboxylic acid Not a ketone-alcohol!
Many classes of organic compounds contain a carbonyl group O O R OR' arbonyl group Ester Not a ketone-ether!
Many classes of organic compounds contain a carbonyl group O O R N 2 arbonyl group Amide Note a ketone-amine!
Alkanes General formula for an alkane n 2n+2 Introduction to Alkanes: Methane, 4 Ethane, 2 6 Propane, 3 8
The simplest alkanes Methane ( 4 ) Ethane ( 2 6 ) Propane ( 3 8 ) 4 3 3 3 2 3 bp -160 bp -89 bp -42 No isomers possible for 1, 2, 3 hydrocarbons
Isomeric Alkanes: The Butanes 4 10 General formula for any butane Isomers: same composition, different structures at the constitutional or stereochemical levels
4 10 n-butane (bp -0.4 ) Isobutane (bp 3 2 2 3 ( 3 ) 3 bp -10.2 )
igher n-alkanes Pentane ( 5 12 ) and Beyond n 2n+2 n > 4
3 2 2 2 3 n-pentane n 2n+2 n > 4 3 2 2 2 2 3 n-exane 3 2 2 2 2 2 3 n-eptane
The 5 12 Isomers
5 12 3 2 2 2 3 n-pentane ( 3 ) 2 2 3 Isopentane ( 3 ) 4 Neopentane
ow many isomers? The number of isomeric alkanes increases as the number of carbons increase. There is no simple way to predict how many isomers there are for a particular molecular formula.
Table 2.3 Number of onstitutionally Isomeric Alkanes 4 1 2 6 1 3 8 1 4 10 2 5 12 3 6 14 5 7 16 9
Table 2.3 Number of onstitutionally Isomeric Alkanes 4 1 8 18 2 6 1 9 20 3 8 1 10 22 4 10 2 15 32 5 12 3 20 42 6 14 5 40 82 7 16 9 18 18 18 35 20 35 75 22 75 32 4,347 42 366,319 82 62,491,178,805,831 (~6 x 10 13 isomers!)
6 6 Isomers ow many isomers with the composition 6 6 can you draw?
6 6 Isomers: ow many isomers with the composition 6 6 can you draw?
Structure and Bonding in Alkenes
Structure of Ethylene bond angles: -- = 117 -- = 121 bond distances: = 110 pm = = 134 pm planar
Bonding in Ethylene!!!!! Framework of! bonds Each carbon is sp 2 hybridized
Bonding in Ethylene Each carbon has a half-filled p orbital
Bonding in Ethylene Side-by-side overlap of half-filled p orbitals gives a! bond which makes it very difficult to rotate about the = bond
Isomerism in Alkenes
Isomers Isomers are different compounds that have the same composition (numbers and kinds. of atoms). Since the compounds are different, they must have different structures in the way the atoms are connected or arranged in space
Isomers onstitutional isomers Stereoisomers
Isomers onstitutional isomers Stereoisomers different connectivity same connectivity; different arrangement of atoms in space
Isomers onstitutional isomers Stereoisomers consider the isomeric alkenes of molecular formula 4 8
2 3 3 3 1-Butene 2-Methylpropene 3 3 3 3 cis-2-butene trans-2-butene
2 3 3 3 1-Butene 2-Methylpropene 3 3 onstitutional isomers cis-2-butene
Same connections, different atomic positions in space Stereoisomers 3 3 3 3 cis-2-butene trans-2-butene
Molecular hirality: Enantiomers
Isomers constitutional isomers stereoisomers
Isomers constitutional isomers stereoisomers enantiomers (optical) geometric isomers (cis/trans) hiral structures
hirality A molecule is chiral if its two mirror image forms are not superposable upon one another. A molecule is achiral if its two mirror image forms are superposable.
Bromochlorofluoromethane is chiral Br l It cannot be superposed point for point on its mirror image. F
Bromochlorofluoromethane is chiral Br l l Br F F To show nonsuperposability, rotate this model 180 around a vertical axis.
Bromochlorofluoromethane is chiral Br l l Br F F
Another look
Enantiomers nonsuperposable mirror images are called enantiomers and are enantiomers with respect to each other
hlorodifluoromethane is achiral
hlorodifluoromethane is achiral The two structures are mirror images, but are not enantiomers, because they can be superposed on each other.
Symmetry in Achiral Structures
Symmetry tests for achiral structures Any molecule with a plane of symmetry must be achiral.
Plane of symmetry A plane of symmetry bisects a molecule into two mirror image halves. hlorodifluoromethane has a plane of symmetry.
Plane of symmetry A plane of symmetry bisects a molecule into two mirror image halves. hlorodifluoromethane has a plane of symmetry.
Plane of symmetry A plane of symmetry bisects a molecule into two mirror image halves. 1-Bromo-1-chloro-2-fluoroethene has a plane of symmetry.
Plane of symmetry A plane of symmetry bisects a molecule into two mirror image halves. 1-Bromo-1-chloro-2-fluoroethene has a plane of symmetry.