Chapter 3

An Introduction to Organic Compounds

Nomenclature, Physical Properties, and Representation of Structure

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ALKANESGENERAL FORMULA CnH2n+2

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NAMING ORGANIC MOLECULES

PREFIX-PARENT-SUFFIX

PARENT IS LONGEST CONTINUOUS CARBON CHAIN

SUFFIX-INDICATES FUNCTIONALITY

PREFIX-INDICATES LOCATION AND NAME OF SUBSTITUENT

(BRANCHING)

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NOMENCLATURE OF PREFIX

REMOVAL OF ONE HYDROGEN ATOM FROM AN ALKANE MOLECULE BECOMES AN ALKYL GROUP, A SUBSTITUTENT.

Alkane Alkyl

CH4 CH3-

Methane Methyl

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NAME OF ALKYL GROUPS

• Removing a hydrogen from an alkane results in an alkyl substituent.

• Replace “ane” of alkane with “yl.”

CH3- CH3CH2-

Methyl Ethyl

CH3CH2CH2- (CH3)2CH-

Propyl Isopropyl

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NAME OF ALKYL GROUPS

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NAME OF ALKYL GROUPS

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ALKYL GROUP NAMES

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ALKANE NOMENCLATURE

PREFIX-PARENT-SUFFIX

PARENT IS LONGEST CONTINUOUS CARBON CHAIN

SUFFIX-INDICATES FUNCTIONALITY

PREFIX-INDICATES LOCATION AND NAME OF SUBSTITUENT (BRANCHING)

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RULES OF ALKANE NOMENCLATURE

1. Find the parent hydrocarbon

(a) Find the longest continuous chain of carbon atoms present in the molecule, and use the name of the chain as the parent chain.

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RULES OF ALKANE NOMENCLATURE

(b) If two different chain of equal length are present, choose the one with the larger number of branch points as the parent chain.

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RULES OF ALKANE NOMENCLATURE

2. Number the atoms in the main chain

(a) Number the carbons of the longest chain beginning with the end that is closest to a substituent.

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RULES OF ALKANE NOMENCLATURE

(b) If there is branching an equal distance away from both ends of the parent chain, begin numbering at the end nearer the second branch point (first point of difference principle).

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RULES OF ALKANE NOMENCLATURE

3. Identify and number the substituent

(a) Assign a number to each substituent according to its point of attachment to the main chain.

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RULES OF ALKANE NOMENCLATURE

(b) If there are two substituents on the same carbon, assign them both the same number.

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RULES OF ALKANE NOMENCLATURE

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ALKANESNUMBER OF POSSIBLE ISOMERIC ALKANES,

CnH2n+2

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n Isomers

1 1

2 1

3 1

4 2

5 3

6 5

7 9

8 18

9 35

10 75

15 4347

20 366319

ALKANES

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COMMON vs. IUPAC NOMENCLATURE OF ALKYL GROUPS

(CH3)2CH-

Common name: Isopropyl

IUPAC name: -(1-Methylethyl)

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COMMON vs. IUPAC NOMENCLATURE OF ALKYL GROUPS

Butyl

-(1-Methylpropyl)- -(2-Methylpropyl)-

sec-Butyl or s-Butyl Isobutyl

tert-Butyl or t-Butyl

-(1,1-Dimethylethyl)-

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COMMON vs. IUPAC NOMENCLATURE OF ALKYL GROUPS

Pentyl Isopentyl orIsoamyl or i-Amyl

-(3-Methylbutyl)-

Neopentyl

-(2,2-Dimethylpropyl)- tert-Pentyl or tert-Amyl or t-Amyl

-(1,1-Dimethylpropyl)-21

ALKANES

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IUPAC NOMENCLATURE OF ALKANES

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CYCLOALKANES, CnH2n

Formula: CnH2n; note that two carbons with what were two C-H bonds are now joined to form a ring.

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CYCLOALKANES

Some examples of cycloalkanes:

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CYCLOALKANES

Cis-Trans-Isomerism in CycloalkanesNote that, in acyclic alkanes, free rotation around all of the carbon-carbon single bonds is occurring constantly and rapidly. In contrast, cycloalkanes are locked in a rigid arrangement. This creates cis (same-side) and trans (across) isomerism in cycloalkanes.

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STEREOISOMERS OF CYCLOALKANES

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CYCLOALKANES

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NOMENCLATURE OF CYLOCAKANES

1. Count the number of carbon atoms in the ring and

the number in the largest substituent.

(a) If the number of carbon atoms in the ring is equal to or greater than the number in the largest substituent, the compound is named as an alkyl-substituted cycloalkane.

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NOMENCLATURE OF CYLOCAKANES

(b) If the number of carbon atoms in the largest substituent is greater than the number of carbons in the ring, the compound is named as an cycloalkyl-substituted alkane.

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NOMENCLATURE OF CYLOCAKANES

2. Proper nomenclature of molecule

(a) For alkyl-substituted cycloalkanes, start at a point of attachment and number the substituents on the ring so as to arrive at the lowest sum. When two or more different alkyl groups are present, number them by alphabetical priority.

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NOMENCLATURE OF CYLOCAKANES

(b) If halogens are present, put all substituentsin alphabetical priority.

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COMMON NAMES WITH VARIOUS FUNCTIONALITIES

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