Question

(a) Draw all five isomers of formula(including stereoisomers).

(b) For each structure, show how many types of would appear in the proton NMR spectrum.

(c) For each structure, show how many types ofwould appear in theNMR spectrum.

(d) If an unknown compound of formulashows three types of and three types of ,can you determine its structure from this information?

Short answer

(a)There are five isomers of formula , including stereoisomers, these are the following:

(d)If an unknown compound of formula shows three types of and three types of, then the proposed structure will be 1,1-dibromopropane.

Step-by-step solution

Explanation of part (a):

Isomers are molecules that have the same molecular formula but have a different arrangement of the atoms in space. These molecules differ in properties and the arrangement of atoms. Structural and stereoisomerism are two types of isomerism which can be further classified into different subtypes. Including stereoisomers, there are total five isomers of formula , these are:

Explanation of part (b):

Proton-NMR is the technique which can help us confirm the structure of organic compounds. Multiplicity in NMR provides the information about the proton neighbors for a particular atom or group of atoms. Number of protons which appear in proton-NMR spectrum of the isomers of molecular formula have been marked a,b,c,d in the following structures:

In structure-3 and 4, there are four types of hydrogen that would give signal in proton-NMR spectrum. Due to presence of chiral center, the adjacent protons of methylene group become diastereotopic which would give different signal in proton-NMR spectrum.

Explanation of part (c):

In carbon-NMR spectrum, each peak identifies a carbon atom in a different environment within the molecule. If two or more carbon atoms in a compound have exactly the same environment, then they will be represented by a single line. Number of carbons which appear in carbon-NMR spectrum of the isomers of molecular formula have been marked a,b,c in the following structures:

Explanation of part (d):

Three types of hydrogen and three types of carbons can be only one isomer, that is, 1,1-dibromopropane. It has three types of hydrogens that would give different signals of different chemical shifts in proton-NMR spectrum and three types of carbon atoms that would give different signals in carbon-NMR spectrum.

Structure of compound having three types of hydrogen and three types of carbon atoms