Question

Week 10- Constitutional isomers Constitutional isomers have the same molecular formula, but their atoms are bonded in different orders. These may be further distinguished as chain isomers, which differ only in hydrocarbon chain structure, positional isomers, which differ in the location of a functional group, and functional group isomers which differ in the nature of their functional groups. Typically chain and position isomers show only modest differences in their physical and chemical properties, while functional group isomers differ greatly from one another. Isomer Type Molecular Formula Structural Formula Boiling Point (°C) CH3CH2CH2CH3 0 chain CH10 (CH3)3CH -12 CH3CH2CH2C1 47 positional C3H7C1 CH3CHCICH 37 CH3CH2OH 78 functional group C2H60 CH3OCH3 -24 A. Chain Isomerism: 1. Butane (C4H10) a) Two isomers of butane exist. Draw Lewis structures for each and provide IUPAC names. b) Prepare model of two isomers. c) What type of isomers are these? d) A carbon atom attached to only one other carbon is called a primary (19) carbon. A carbon

Answer 1

Answer of 1 Butane a):

A Lewis Structure is simplified representation of the valence shell electrons in a molecule. It is used to show how the electrons are arranged around individual atoms in a molecule. Electrons are shown as "dots" or for bonding electrons as a line between the two atoms.

Butane has two isomers and their Lewis structures and their names are

H H H H H HC-H .HH H H-C-C-C- CH H H C-C 2 3 I H H H H H H Butane 2-Methylpropane

The name butane because it contains 4 carbons for 4 carbons the name is butane.

The second isomer methyl group present at 2 position and basic chain contains 3 carbon so the name is 2-Methylpropane.

Answer of 1 Butane b): Models of Butane and 2-Methylpropane

Carbon atom Hydrogen atom sigma bond HH + Butane 2-Methylpropane

Answer of 1 Butane c): These isomers are differ in chain length i.e. butane have 4 carbon chain amd 2-Methyl have 3 carbon chain.Such a isomers are referred as chain or nuclear isomers.

CH3 ( HzC—CH2 - CH2 - CH3 ) | H3C—CH-CH3 ) 4 carbon chain 3 carbon chain

Answer of 1 Butane d):

CH3 CH3 CH3 i) H2C=CH2 ii) HzC H3C—C—CH3 iii) H3C-CH2-CH2 iv) (CH3)3CH H3C-C-H CH3 CH3 n-butane H isobutane CH3 n-butane isobutane CH3 v) CH3(CH2)2CH3 H3C-CH2-CH2-CH3 vi) CH3CH(CH3)2 H3C-CH-CH3 n-butane isobutane

Answer of 2 Pentane a):

Three possible chain isomers of pentane are n-pentane, 2-Methylbutane and 2,2-Dimethylpropane. Their Lewis structures and IUPAC names are as follow.

Only 2,2-Dimethylpropane molecule has no secondary and tertiary carbonswhich is shown by circle.

H H Н ннн \, Н. н Н Hн H Н. Н. 10 H 10 10 10 H— С Н. С С. С. -Н С H -С 20 С. 10 Н. — С С С Н 1| 20 29 С. 10 49 20 H 30 Н. Н H Н Н 19 H Н Н. H n-pentane 2-methylbutane н 19 С. н Н Н 2,2-Dimethylpropane

Answer of 2 Pentane b): Models of three chain isomers of pentane.

carbon atom hydrogen atom sigma bond #本 y n-pentane 2-methylbutane 2,2-Dimethylpropane

Answer of 3 Cyclopentane a):

By arranging 5 carbons in ring 5-membered ring is formed this is called as cyclopentane.

Answer of 3 Cyclopentane b):

Cyclopentane and pentane are not the isomers because the isomers are those compounds having same molecular formula. Here the cyclopentane molecular formula is C₅H₁₀ whereas pentane has molecular formula is C₅H₁₂. So these two are not isomers of each others.