1. Structure of hydrocarbons
Hydrocarbon: a compound composed only of carbon and hydrogen
Saturated hydrocarbon: a hydrocarbon containing only single bonds
Alkane: a saturated hydrocarbon whose carbons are arranged in an open chain
Aliphatic hydrocarbon: another name for an alkane

2. Hydrocarbons

3. Structure Shape tetrahedral about carbon
all bond angles are approximately 109.5°

4. Drawing Alkanes Line-angle formulas
an abbreviated way to draw structural formulas
each vertex and line ending represents a carbon

5. Constitutional Isomerism
Constitutional isomers: compounds with the same molecular formula but a different connectivity of their atoms
example: C4H10

6. Constitutional Isomerism
do these formulas represent constitutional isomers?
find the longest carbon chain
number each chain from the end nearest the first branch
compare chain lengths as well the identity and location of branches

7. Constitutional Isomerism
World population
is about
6,000,000,000

8. Nomenclature - IUPAC Suffix -ane specifies an alkane
Prefix tells the number of carbon atoms

9. Nomenclature - IUPAC Parent name: the longest carbon chain
Substituent: a group bonded to the parent chain
alkyl group: a substituent derived by removal of a hydrogen from an alkane; given the symbol R-

10. Nomenclature - IUPAC
1.The name of a saturated hydrocarbon with an unbranched chain consists of a prefix and suffix 2. The parent chain is the longest chain of carbon atoms 3. Each substituent is given a name and a number 4. If there is one substituent, number the chain from the end that gives it the lower number

11. Nomenclature - IUPAC
5. If there are two or more identical substituents, number the chain from the end that gives the lower number to the substituent encountered first
indicate the number of times the substituent appears by a prefix di-, tri-, tetra-, etc.
use commas to separate position numbers

12. Nomenclature - IUPAC
6. If there are two or more different substituents,
list them in alphabetical order
number from the end of the chain that gives the substituent encountered first the lower number

13. Nomenclature - IUPAC
7. The prefixes di-, tri-, tetra-, etc. are not included in alphabetization
alphabetize the names of substituents first and then insert these prefixes

14. Nomenclature - IUPAC
Alkyl groups

15. Nomenclature - Common
The number of carbons in the alkane determines the name
all alkanes with four carbons are butanes, those with five carbons are pentanes, etc.
iso- indicates the chain terminates in -CH(CH3)2; neo- that it terminates in -C(CH3)3

16. Classification of C & H
Primary (1°) C: a carbon bonded to one other carbon
1° H: a hydrogen bonded to a 1° carbon
Secondary (2°) C: a carbon bonded to two other carbons
2° H: a hydrogen bonded to a 2° carbon
Tertiary (3°) C: a carbon bonded to three other carbons
3° H: a hydrogen bonded to a 3° carbon
Quaternary (4°) C: a carbon bonded to four other carbons

17. Cycloalkanes General formula CnH2n
five- and six-membered rings are the most common
Structure and nomenclature
to name, prefix the name of the corresponding open-chain alkane with cyclo-, and name each substituent on the ring
if only one substituent, no need to give it a number
if two substituents, number from the substituent of lower alphabetical order
if three or more substituents, number to give them the lowest set of numbers and then list substituents in alphabetical order

18. Cycloalkanes Line-angle drawings each line represents a C-C bond
each vertex and line ending represents a C

19. Cycloalkanes
Example: name these cycloalkanes

20. IUPAC - General Nature of Carbon-Carbon Bonds in the Parent Chain
prefix-infix-suffix
prefix tells the number of carbon atoms in the parent
infix tells the nature of the carbon-carbon bonds
suffix tells the class of compound
Nature of Carbon-Carbon
Bonds in the Parent Chain
Suffix
Class
Infix -e
hydrocarbon
-an-
all single bonds
-ol
alcohol
-en-
one or more double bonds
-al
aldehyde
-yn-
one or more triple bonds
-amine
amine
-one
ketone
-oic acid
carboxylic acid

21. IUPAC - General
prop-en-e = propene eth-an-ol = ethanol but-an-one = butanone but-an-al = butanal pent-an-oic acid = pentanoic acid cyclohex-an-ol = cyclohexanol eth-yn-e = ethyne eth-an-amine = ethanamine

22. Cis,Trans Isomerism Stereoisomers: compounds that have
the same molecular formula
the same connectivity
a different orientation of their atoms in space
Cis,trans isomers
stereoisomers that are the result of the presence of either a ring (this chapter) or a carbon-carbon double bond (Chapter 5)

23. Isomers
relationships among isomers

24. Cis,Trans Isomers
1,2-Dimethylcyclopentane

25. Cis,Trans Isomerism
1,4-Dimethylcyclohexane

26. Cis,Trans Isomerism trans-1,4-Dimethylcyclohexane
the diequatorial-methyl chair conformation is more stable by approximately 2 x (7.28) = kJ/mol

27. Cis,Trans Isomerism
cis-1,4-Dimethylcyclohexane

28. Physical Properties
Constitutional isomers have different physical properties

29. Heats of Combustion For constitutional isomers [kJ (kcal)/mol]
( )
( )
(1304.6)
(1303.0) 8 C O 2 + 9 H 2 O

30. Heat of Combustion
strain in cycloalkane rings as determined by heats of combustion

31. Sources of Alkanes Natural gas Petroleum Coal 90-95% methane
gases (bp below 20°C)
naphthas, including gasoline (bp °C)
kerosene (bp °C)
fuel oil (bp °C)
lubricating oils (bp above 350°C)
asphalt (residue after distillation)
Coal

32. Gasoline
Octane rating: the percent 2,2,4-trimethylpentane (isooctane) in a mixture of isooctane and heptane that has equivalent antiknock properties

33. Unsaturated Hydrocarbons
Unsaturated hydrocarbon: contains one or more carbon-carbon double or triple bonds
Alkene: contains a carbon-carbon double bond and has the general formula CnH2n

34. Unsaturated Hydrocarbons
Alkyne: contains a carbon-carbon triple bond and has the general formula CnH2n-2

35. Unsaturated Hydrocarbons
Arenes: benzene and its derivatives

36. Benzene & Phenyl Group
the phenyl group is not reactive under any of the conditions we describe for alkynes

37. Structure of Alkenes
The two carbon atoms of a double bond and the four atoms attached to them lie in a plane, with bond angles of approximately 120°
According to the orbital overlap model, a double bond consists of
one sigma bond formed by overlap of sp2 hybrid orbitals
one pi bond formed by overlap of parallel 2p orbitals

38. Structure of Alkenes
Length of C-C bonds: single > double > triple
Strength of C-C bonds:triple > double > single

39. Cis-Trans Isomerism
Because of restricted rotation about a C-C double bond, groups on adjacent carbons are either cis or trans to each other

40. Nomenclature - Alkenes
Use the infix -en- to show the presence of a carbon-carbon double bond
Number the parent chain to give the 1st carbon of the double bond the lower number
Follow IUPAC rules for numbering and naming substituents
For a cycloalkene, the double bond must be numbered 1,2

41. Nomenclature - Alkenes

42. Nomenclature - Alkenes

43. Nomenclature - Alkenes
Some alkenes, particularly low-molecular-weight ones, are known almost exclusively by their common names

44. Nomenclature - Alkynes
IUPAC: use the infix -yn- to show the presence of a carbon-carbon triple bond

45. Nomenclature - Alkynes
Common names: prefix the substituents on the triple bond to the name “acetylene”

46. Configuration - cis, trans
The cis-trans system: configuration is determined by the orientation of atoms of the main chain

47. Configuration - E,Z
The E,Z system uses the priority rules of the R,S system to assign to the groups on each carbon of a carbon-carbon double bond
1. Each atom bonded to the C-C double bond is assigned a priority
2. If groups of higher priority are on the same side, configuration is Z (German, zusammen)
3. If groups of higher priority are on opposite sides, configuration is E (German, entgegen)

48. Configuration - E,Z
Example: name each alkene and specify its configuration by the E,Z system

49. Physical Properties Alkenes are nonpolar compounds
The only attractive forces between their molecules are dispersion forces
The physical properties of alkenes are similar to those of alkanes

50. Terpenes
Terpene: a compound whose carbon skeleton can be divided into two or more units identical with the carbon skeleton of isoprene

51. Terpenes
Myrcene, C10H16, a component of bayberry wax and oils of bay and verbena
Menthol, from peppermint
Camphor, from the camphor tree

52. Vitamin A (Retinol)

53. Benzene - Resonance Model
The concepts of hybridization of atomic orbitals and the theory of resonance, developed in the 1930s, provided the first adequate description of benzene’s structure and reactivity
the carbon skeleton is a regular hexagon
all C-C-C and H-C-C bond angles 120°

54. Benzene - The Resonance Model
The pi system of benzene
(a) the carbon framework with the six 2p orbitals
(b) overlap of the parallel 2p orbitals forms one torus above the plane of the ring and another below it
this orbital represents the lowest-lying pi-bonding molecular orbital

55. Benzene - Resonance
We often represent benzene as a hybrid of two equivalent Kekulé structures
each makes an equal contribution to the hybrid and thus the C-C bonds are neither double nor single, but something in between

56. Benzene - Resonance
Resonance energy: the difference in energy between a resonance hybrid and the most stable of its hypothetical contributing structures in which electrons are localized on particular atoms and in particular bonds
one way to estimate the resonance energy of benzene is to compare the heats of hydrogenation of benzene and cyclohexene

57. Benzene

58. Concept of Aromaticity
The underlying criteria for aromaticity were recognized in the early 1930s by Erich Hückel, based on molecular orbital (MO) calculations
To be aromatic, a compound must
be cyclic
have one p orbital on each atom of the ring
be planar or nearly planar so that there is continuous or nearly continuous overlap of all p orbitals of the ring
have a closed loop of (4n + 2) pi electrons in the cyclic arrangement of p orbitals

59. Heterocyclic Aromatics
Heterocyclic compound: a compound that contains more than one kind of atom in a ring
in organic chemistry, the term refers to a ring with one or more atoms are other than carbon
Pyridine and pyrimidine are heterocyclic analogs of benzene; each is aromatic.

60. Nomenclature of aromatic compounds
Monosubstituted alkylbenzenes are named as derivatives of benzene
many common names are retained T
oluene E
thylbenzene C
umene S
tyrene O H N H 2 C H O C O H O C H 3
Phenol
Aniline
Benzaldehyde
Benzoic acid
Anisole

61. Nomenclature Benzyl and phenyl groups C H C H - Benzene P3 C H 2 -
Benzene P
henyl group, Ph-
Toluene B
enzyl group, Bn- O O H 3 C O P h
1-Phenyl-1pentanone
4-(3-Methoxyphenyl)-
2-butanone
(Z)-2-Phenyl-
2-butene

62. Disubstituted Benzenes
Locate two groups by numbers or by the locators ortho (1,2-), meta (1,3-), and para (1,4-)
where one group imparts a special name, name the compound as a derivative of that molecule

63. Polysubstituted Derivatives
if one group imparts a special name, name the molecule as a derivative of that compound
if no group imparts a special name, list them in alphabetical order, giving them the lowest set of numbers C H 3 O H N O 2 1 1 N O 2 B r B r 4 2 6 2 2 B r 4 4 1 C l B r C H 2 3
4-Chloro-2-nitro-
toluene
2,4,6-Tribromo-
phenol
2-Bromo-1-ethyl-4-
nitrobenzene

64. Phenols
The functional group of a phenol is an -OH group bonded to a benzene ring O H O H O H O H O H C H 3 O H
Phenol
3-Methylphenol ( m-
Cresol)
1,2-Benzenediol
(Catechol)
1,4-Benzenediol
(Hydroquinone)

65. Phenols hexylresorcinol is a mild antiseptic and disinfectant
eugenol is used as a dental antiseptic and analgesic
urushiol is the main component of the oil of poison ivy

66. Quinones
Important chemical property of quinones is that they are readily reduced to hydroquinones