jazz_xox_
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#1
Report Thread starter 3 years ago
#1
I was doing the specimen paper and there's some basic isomerism questions that I just wanted clarification with

Isooctane (C8H18) is the common name for the branched-chain hydrocarbon that burns smoothly in car engines

The skeletal formula is given but it is 2,2,4-trimethylpentane

Deduce the number of monochloro isomers formed by isooctane. Draw the structure of the monochloro isomer that exists as a pair of optical isomers.
I got this right but just wanted to double check- can the chlorine only subsitution for a single H atom on isooctane? - hence 4 monochloroisomers can form. Also, how would the chlorines join here? (that's not required and I'm not sure if we'd need it, just for future reference)

An isomer of isooctane reacts with chlorine to form only one monochloro compound. Draw the skeletal formula of this monochloro compound.
This is the bit I'm confused on. Would this be if there is only 1 single hydrogen atom on the molecule to substitue?
I put down the molecule of 2,chloro, 3,3,dimethylbutane but my skeletal formula doesn't look like the one on the mark scheme- so confused if it's the same thing.

http://filestore.aqa.org.uk/resource...-74052-SMS.PDF
It's question 3.6

Thank you!
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faith43211
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#2
Report 3 years ago
#2
Also need help on this question, did you even get it?
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Organics
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#3
Report 3 years ago
#3
Sorry this is a bit late,

If only one mono chloro isomer is to be formed, all H atoms must be in the same environment, so that they will give the same substitution product if replaced by a Cl atom. So we must have an octane isomer in which all hydrogens are in the same environment.

We cannot substitute a Cl at a Quaternary site, as there is no H atom to substitute at these positions.

One possible structure is (2,2,3,3)-tetramethylbutane. Substitution at any position will give (2,2,3,3)-tetramethyl-(1)-chlorobutane, and so only one mono substituted product is formed. The structure you gave only has 6 carbons, and so is not an isomer of Isooctane.

I have attatched a picture of the correct alkane and substitution product.

Name:  octane chloro isomers.png
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