2- Bromopropane chemically equivalent

Protons in the same environment are called chemically equivalent protons. For example, 1-bromopropane has three different sets of chemically equivalent protons. The toee methyl protons are chemically equivalent because of rotation about the C—C bond. The two methylene protons on the middle carbon are chemically equivalent, and the two methylene protons on the carbon bonded to the bromine atom make up the third set of chemically equivalent protons. 

Each set of chemically equivalent protons in a compound gives rise to a signal in the NMR spectrum of that compound. (Sometimes the signals are not sufficiently separated and overlap each other. When this happens, one sees fewer signals than anticipated.) Because 1-bromopropane has three sets of chemically equivalent protons, it has three signals in its NMR spectrum. 

Bromopropane has two sets of chemically equivalent protons and, therefore, it has two signals in its NMR spectrum. The six methyl protons in 2-bromo-propane are equivalent, so they give rise to only one signal. Ethyl methyl ether has three sets of chemically equivalent protons the methyl protons on the carbon adjacent to the oxygen, the methylene protons on the carbon adjacent to the oxygen. 

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