Describe at least four essential features expected in the functional group region (grater then...


Describe at least four essential features expected in the functional group region {eq}(> 1500\ cm^{-1}) {/eq} of the IR spectrum for this compound.

Infrared Spectroscopy

Infrared spectroscopy (IR) involves the interaction of infrared radiation with matter. Functional groups will behave (vibrate, stretch, flex, wiggle, basically move around) at different ranges on the spectra based on the type of functional group. This can be used to identify and study chemical substances.

The width and location of the peak in an IR is indicative of what functional group caused it. Alcohol and carboxylic acid peaks are very broad verses carbonyl peaks which are very narrow and sharp. Substituted benzene rings have peaks that correspond to the substitution pattern (Mono, para, meta, etc) in the fingerprint and overtone regions of the IR.

Aromatic rings have very characteristic peaks that will appear based on the substitution patter of the ring. These peaks appear in the fingerprint region of the IR (900-670{eq}cm^{-1} {/eq}) and have a very strong to moderate intensity. In the overtone region (2000-1650{eq}cm^{-1} {/eq}), a pattern can also form that will further support the aromatic substitution pattern, but these peaks are very weak. Since carbonyl peaks also appear in this region, the overtone pattern might be drowned out by more intense peaks. See the table below for the key peaks to look for.

Answer and Explanation:

There are 5 characteristic peaks in this structure.

  1. Peaks in the 3100-3010{eq}cm^{-1} {/eq} region caused by the {eq}sp^{2} {/eq} C-H on the...

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Infrared Spectroscopy & Molecule Identification
Infrared Spectroscopy & Molecule Identification

from AQA A-Level Chemistry: Practice and Study Guide

Chapter 2 / Lesson 13

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