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An unknown liquid (A) showed no IR absorption between 1500 and 2500 cm^{-1}. Similarly there was...

Question:

An unknown liquid {eq}(A) {/eq} showed no {eq}IR {/eq} absorption between {eq}1500 {/eq} and {eq}2500 \ cm^{-1}. {/eq} Similarly there was no absorption above {eq}3000 \ cm^{-1}. {/eq} Compound {eq}A {/eq} reacted with alcoholic silver nitrate to give cloudiness after serval minutes and it also reacted with sodium iodide in acetone to give a precipitate after several minutes. What conclusion can be made about the identity of compound {eq}A {/eq}?

IR peaks and Alkyl halide :

IR (infrared) is a type of spectroscopy used to determine the structure of the unknown compound and also the purity of the compound formed.

It is mainly used to detect the functional groups.

Alkyl halide that is carbon halogen bonds appear at 500-600{eq}cm^{-1} {/eq} and for fluorine it is around 1000{eq}cm^{-1} {/eq}

Answer and Explanation: 1

As the unknown compound has no IR peak between 1500 to 2500 {eq}cm^{-1} {/eq}, that means there is of carbon-carbon double bond and triple bond. Also the carbonyl and cyanide functional groups is absent.

Also, there is no peak over 3000{eq}cm^{-1} {/eq} that suggest it does not have alcohol and amines as functional group.

This suggest that there is a possibility of alkyl halide or a simple hydrocarbon.

Now, on reacting with alcoholic silver nitrate it produces cloudiness suggets it can be a alkylbromide, as alkyl iodide produces instant precipitate and a chloro compound takes really long time.

Also the alkyl group can be secondary as tertiary produces instant precipitate and primary takes long time.

Now reaction with sodium iodide gives precipitate that means chlorine or bromine is replaced by iodine.So the halide can be bromine or chlorine.

And the reaction is fast for primary halides.

The reactions taking place can be -

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Learn more about this topic:

Alkyl Halide: Structure & Reactions
Alkyl Halide: Structure & Reactions

from

Chapter 2 / Lesson 8
20K

Learn about the alkyl halide structure and the definition of halide. See alkyl halide examples and find out more about their reactions in this engaging lesson.


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