Organic Chemistry

62 CHAPTER 2 An Introduction to Organic Compounds

There are three alkanes with molecular formula Pentane is the straight-

chain alkane. Isopentane, as its name indicates, has an iso structural unit and five car-

bon atoms. The third isomer is called neopentane. The structural unit with a carbon

surrounded by four other carbons is called “neo.”

There are five constitutional isomers with molecular formula We are now

able to name three of them (hexane, isohexane, and neohexane), but we cannot name

the other two without defining names for new structural units. (For now, ignore the

names written in blue.)

C 6 H 14.

CH 3 CH 2 CH 2 CH 2 CH 3

pentane

CH 3 CHCH 2 CH 3

isopentane

CH 3

CH 3 CCH 3

neopentane

CH 3

CH 3

CH 3 CCH 2

CH 3

CH 3

a “neo”

structural unit

C 5 H 12.

Table 2.1 Nomenclature and Physical Properties of Straight-Chain Alkanes

Number Boiling Melting

of Molecular Condensed point point Densitya

carbons formula Name structure (°C) (°C) (g mL)

1 methane

2 ethane

3 propane

4 butane

5 pentane 36.1 0.5572

6 hexane 68.7 0.6603

7 heptane 98.4 0.6837

8 octane 127.7 0.7026

9 nonane 150.8 0.7177

10 decane 174.0 0.7299

11 undecane 195.8 0.7402

12 dodecane 216.3 0.7487

13 tridecane 235.4 0.7546

20 eicosane 343.0 36.8 0.7886

21 heneicosane 356.5 40.5 0.7917

30 triacontane 449.7 65.8 0.8097

aDensity is temperature dependent. The densities given are those determined at 20 °C 1 d 20 ° 2.

C 30 H 62 CH 3 (CH 2 ) 28 CH 3

o o o o o o o

C 21 H 44 CH 3 (CH 2 ) 19 CH 3

C 20 H 42 CH 3 (CH 2 ) 18 CH 3

o o o o o o o

C 13 H 28 CH 3 (CH 2 ) 11 CH 3 - 5.5

C 12 H 26 CH 3 (CH 2 ) 10 CH 3 - 9.6

C 11 H 24 CH 3 (CH 2 ) 9 CH 3 - 25.6

C 10 H 22 CH 3 (CH 2 ) 8 CH 3 - 29.7

C 9 H 20 CH 3 (CH 2 ) 7 CH 3 - 53.5

C 8 H 18 CH 3 (CH 2 ) 6 CH 3 - 56.8

C 7 H 16 CH 3 (CH 2 ) 5 CH 3 - 90.6

C 6 H 14 CH 3 (CH 2 ) 4 CH 3 - 95.3

C 5 H 12 CH 3 (CH 2 ) 3 CH 3 - 129.8

C 4 H 10 CH 3 CH 2 CH 2 CH 3 - 0.5 -138.3

C 3 H 8 CH 3 CH 2 CH 3 - 42.1 -187.7

C 2 H 6 CH 3 CH 3 - 88.6 -183.3

CH 4 CH 4 - 167.7 -182.5

>

CH 3 CH 2 CH 2 CH 2 CH 2 CH 3

hexane

hexane

CH 3 CHCH 2 CH 2 CH 3

isohexane

2-methylpentane

CH 3

CH 3 CH 2 CHCH 2 CH 3

3-methylpentane

CH 3

CH 3 CH CHCH 3

2,3-dimethylbutane

CH 3 CH 3

CH 3 CCH 2 CH 3

neohexane

2,2-dimethylbutane

CH 3

CH 3

common name:

systematic name:

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