Spectroscopic analysis:

The alkyl halides' IR spectra generally show strong C-X stretching absorptions. The position of these absorptions depends upon the halogen involved that is the absorptions for C-F, C-Cl, C-Br and C-I take place in the regions 1400-1000, 800-600, 750-500 and 500 cm^-1 correspondingly. The existence of a halogen can occasionally be implicated by the chemical shifts of neighboring groups in the nmr spectra. For instance the chemical shifts in the ¹H nmr spectrum for CH₂I, CH₂Br and CH₂Cl are 3.2, 3.5 and 3.6 correspondingly. Good proof for the existence of a halogen emerges from elemental analysis and mass spectroscopy. In later, there are characteristic peak patterns related with specific halogens as a result of the natural abundance of several isotopes. For instance, bromine has two naturally occurring isotopes of 79 and 81 that take places in a ratio of 1: 1. This means that two peaks of equivalent intensity will be present for any organic compound consisting of bromine. For instance, the mass spectrum for ethyl bromide has two peaks of equivalent intensity at m/e 108 and 110 for the molecular ions ¹²C₂ ¹H₅ ⁷⁹Br and ¹²C₂ ¹H₅ ⁸¹Br correspondingly.

In difference, chlorine takes place naturally as two isotopes (³⁵Cl and ³⁷Cl) in the ratio 3: 1. The meaning of this is that the mass spectrum of a compound consisting of a chlorine atom will have two peaks for the molecular ion. These peaks will be 2 mass units apart with an intensity ratio of 3: 1.