Answer
a. three (03) isomers can be obtained when one H is replaced by a chlorine atom for n-pentane.
b. four (04) isomers can be obtained when one H is replaced by a chlorine atom for 2-methylbutane.
c. three (03) isomers isomers can be obtained when one H is replaced by a chlorine atom for 2,4-dimethylpentane.
d. four (04) isomers can be obtained when one H is replaced by a chlorine atom for methylcyclobutane.
Work Step by Step
a. Draw the structure of n-pentane. We see that the three H attached with C1 carbon are equivalent. So, one isomer (1-chloropentane) is obtained when one of the three Hydrogen atoms are replaced. two H attached with C2 carbon are equivalent. So, another isomer(2-chloropentane) is obtained when one of the two hydrogens are replaced on C2 carbon. Similarly, for C3 carbon two H atoms are equivalent. So, another isomer(3-chloropentane) is obtained. Hydrogen atoms of C4 and C5 carbon become similar to C2 and C1 carbon when H is replaced. So, total no. of isomer obtained = 3.
b. Draw the structure of 2-methylbutane. First, consider the H attached with straight chain C atoms. one of the H atoms from C1 carbon can be replaced to obtain an isomer(1-chloro-2-methylbutane). One H atom from C2 carbon can be replaced to obtain another isomer (2-chloro-2-methylbutane). One of the H atoms from C3 carbon can be replaced to obtain another isomer (3-chloro-2-methylbutane) and one of the H atoms from C4 carbon can be replaced to obtain another isomer(4-chloro-2-methylbutane). Now, if we consider the H atoms present in the substituent methyl and replaced one H with Cl, the isomer is identical with the first isomer (1-chloro-1-methylbutane). So, total no. of isomer obtained = 4.
c. Draw the structure of 2,4-dimethylpentane. First, consider the H attached with straight chain C atoms. one of the H atoms from C1 carbon can be replaced to obtain an isomer (1-chloro-2,4-dimethylpentane). One H atom from C2 carbon can be replaced to obtain another isomer (2-chloro-2,4-dimethylpentane). One of the H atoms from C3 carbon can be replaced to obtain another isomer (3-chloro-2,4-dimethylpentane). Now, if we consider the H atoms present in C4 carbon and replaced one H with Cl, the isomer is identical with the second isomer (2-chloro-2,4-dimethylpentane). similarly, if we consider the H atoms present in C5 carbon and replaced one H with Cl, the isomer is identical with the first isomer (1-chloro-2,4-dimethylpentane). Now, if we consider the H atoms present in substituent methyl at C2 and replaced one H with Cl, the isomer is identical with the first isomer(1-chloro-2,4-dimethylpentane). Similarly, if we consider the H atoms present in substituent methyl at C4 carbon and replaced one H with Cl, the isomer is identical with the first isomer(1-chloro-2,4-dimethylpentane). So, total no. of isomer obtained = 3.
c. Draw the structure of methylcyclobutane. First, consider the H attached with ring C. one H atom from C1 carbon can be replaced to obtain an isomer (1-chloro-1-methylcyclobutane). One of the H atoms from C2 carbon can be replaced to obtain another isomer (2-chloro-1-methylcyclobutane). One of the H atoms from C3 carbon can be replaced to obtain another isomer (3-chloro-1-methylcyclobutane). Now, if we consider the H atoms present in the C4 carbon, the isomer obtained is identical with second isomer(2-chloro-1-methylcyclobutane). Now, consider the H atoms present in the substituent methyl and replace with Cl atom, we will get another isomer(1-chloromethylcyclobutane). so, total no. of isomer obtained = 4.
