Contents

Structure and Nomenclature of Simple
Hydrocarbons Organic Compounds (
Alkanes , alkenes and their Cyclic
Compounds )

Constitution – Configuration – Conformation
1
Alkanes: Nomenclature
Organic nomenclature is based on alkanes:

Contain only carbon and hydrogen (C, H).

All carbon atoms are sp3 hybridized.
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Chapter 2
2
Alkanes - Isomerism
Number of
Carbons
6
Molecular
Formula
C6H14
Number of
Isomers
5
7
C7H16
9
12
C12H26
75
15
C15H32
4347
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Chapter 2
3
Nomenclature

The International Union of Pure and Applied Chemistry (IUPAC) has
established the nomenclature system.

Systematic nomenclature (IUPAC nomenclature) (shown in blue).

Additional names such as isopentane and neopentane are common
names (dt.: Trivialnamen; shown in red).

A compound may have more than one name
but a name must specify only one compound.
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Chapter 2
4
Conformations of Alkanes:
Rotation about C-C Single Bonds

Different spatial arrangements of atoms that result from rotation
about carbon-carbon single bonds are known as conformations.

Different conformations also are called conformational isomers or
conformers:
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Chapter 2
5
Newman Projections

A convenient way to describe conformation isomers is to look at the
molecule along the axis of the bond of interest.

A Newman projection is a graphical representation of such a view:
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Chapter 2
6
Conformations of Alkanes:
Rotation About C-C Single Bonds

When ethane molecules rotate about the carbon-carbon single bond
various isomers result, two of them are:
staggered or anti conformation
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eclipsed or syn conformation.
Chapter 2
7
Conformations of Alkanes:
Rotation About C-C Single Bonds
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Chapter 2
8
Conformations of Alkanes:
Rotation About C-C Single Bonds

The extra energy of the eclipsed conformation is called torsional strain:
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Chapter 2
9
Conformations of Butane:
Rotation About the C2-C3 Single Bond
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Chapter 2
10
Conformations of Butane:
Rotation About the C2-C3 Single Bond
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Chapter 2
11
Nomenclature

Typically, any unspecified alkyl group is represented as R© Prentice Hall 2001
Chapter 2
12
Nomenclature

1. Rule:
Count the longest continuous straight chain to constitute a compound name:
Note that these compounds all have the
same sum formula C7H16;
they are isomers.
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Chapter 2
13
Nomenclature of Alkyl Substituents

The name of the alkyl group followed by the name of the class of
compound constitutes the common name for alcohols amines, and
alkyl halides:
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Chapter 2
14
Alkyl Nomenclature

A primary carbon is one that is bonded to only one other carbon,
frequently represented by 1

A primary hydrogen is attached to a primary carbon:
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Chapter 2
15
Alkyl Nomenclature

A secondary carbon is one that is bonded to two other carbons,
represented by 2, also by sec- or s-

A secondary hydrogen is attached to a secondary carbon:
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Chapter 2
16
Alkyl Nomenclature

A tertiary carbon is one that is bonded to three other carbons,
represented by 3, also by tert- or t-

A tertiary hydrogen is attached to a tertiary carbon:

Reactivity often depends on whether a carbon or hydrogen is 1,
2, or 3!
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Chapter 2
17
Nomenclature of Alkyl Substituents

There are four alkyl groups that contain four carbons:
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Chapter 2
18
Nomenclature of Alkyl Substituents
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Chapter 2
19
IUPAC Systematic Nomenclature:
Alkanes
1.
Determine longest continuous chain (i.e. parent hydrocarbon).
2.
Cite the name of substituent before the name of the parent
hydrocarbon along with the number of the carbon to which it is
attached:
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Chapter 2
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IUPAC Systematic Nomenclature:
Alkanes
3.
Number in the direction that gives the lower number for the
lowest-numbered substituent.
4.
Substituents are listed in alphabetical order – neglecting
prefixes such as di- tri- tert- etc.
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IUPAC Systematic Nomenclature:
Alkanes
4.
When both directions yield the
same lower number for the
lowest numbered substituent,
select the direction that yields
the lower number for the next
lowest numbered substituent:
5.
If same substituent numbers are
obtained in either direction,
number in direction giving lowest
number to the first named
substituent.
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Chapter 2
22
IUPAC Systematic Nomenclature:
Alkanes
6.
If compound has two or more chains of the same length, parent
hydrocarbon is chain with higher number of substituents:
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Chapter 2
23
Nomenclature of Cycloalkanes

Cycloalkanes generally are shown as skeletal structures:
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Chapter 2
24
Nomenclature of Cycloalkanes
1.
Ring is the parent hydrocarbon unless the alkyl substituent has
more carbons; in that case the substituent becomes the parent
hydrocarbon.
If only one substituent, no need to give it a number:
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Chapter 2
25
Nomenclature of Cycloalkanes
2.
If the ring has 2 substituents, list in alphabetical order and give
number 1 to first named group:
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Chapter 2
26