Chapter 21.2, Problem 16SSC

Interpretation Introduction

Interpretation:

The reason for incorrect name, 3-butylpentane needs to be explained and the structural formula of this compound needs to be determined along with its correct IUPAC name.

Concept introduction:

The hydrocarbon compounds that contains single bond(s) between carbon atom(s) are said to be saturated hydrocarbon. Hydrocarbon compounds containing single bonds only are said to be alkane.

Explanation of Solution

Alkanes are compounds containing carbon and hydrogen atoms having single bond(s) between carbon atom(s) in the structure. For number of carbons atoms in alkane chain, the prefix is given as:

Carbon-1   meth

Carbon-2   eth

Carbon-3   prop    

Carbon-4   but      

Carbon-5   pent

Carbon-6   hex

Carbon-7   hept

Carbon-8   oct

Carbon-9   non     

Carbon-10       dec

The numbering of the carbon chain is done in such a way that substituents gets lower number.

The given name is 3-butylpentane that means the parent chain has 5 number of carbons in the chain and -butyl represents the presence of butyl substituent at position 3. So, the structure of 3-butylpentane is:

The name, 3-butylpentane is wrong as, according to IUPAC rule the longest chain is the parent chain in the compound and rest are present as substituents on the compound. So, the parent chain will be carbon atoms with 7 carbons in the longest chain and ethyl substituent at 3-position as shown:

Hence, the correct IUPAC name for the compound is, 3-ethylheptane.