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It is a multiple choice question:

Which compound does not show stereoisomerism?

A 1,2-dichloroprop-1-ene

B 1,2-dichloropropane

C 1,3-dichloroprop-1-ene

D 1,3-dichloropropane

I can eliminate A and C as they show geometrical isomerism as there is a double bond with different priority groups on either side so these can form E and Z isomers.

Leaving B and D and by the nature being an alkane means that they cannot have geometrical isomerism as they have no double bond. Leaving us to identify which one, therefore, has optical isomerism. Which occurs from my understanding from a chiral center where a carbon is bonded to four different groups. But I cant apply this knowledge to understand why it is D as carbons in B and D are bonded to four atoms so surely they both show optical isomerism which is incorrect given the answer.

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    $\begingroup$ A carbon in methane is bonded to 4 atoms too. Do you understand why there is no isomerism here? $\endgroup$ – Ivan Neretin Oct 13 '18 at 7:57
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In option number D, the 3rd carbon is attached to 2 hydrogen atoms. This immediately provides your answer. For optical isomerism, case is: Carbon should be attached to 4 different atoms or group of atoms.

For B, the central(number 2) carbon is attached with Cl atom, H atom, CHCl group and CH3 group which are all different, and thus shows optical isomerism. Again implying your answer is D.

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This is definition of a chiral center.

A chiral centre is an atom that has four different groups bonded to it in such a manner that it has a nonsuperimposable mirror image.

For example:

enter image description here

Carbon at second position in 1,2-dichloropropane is chiral, as all atoms attached to it are different.

1,2-dichloropropane

Whereas 1,3-dichloropropane does not have any chiral center.

1,3-dichloropropane

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    $\begingroup$ good, but please use PNG images, to prevent noise garbage. $\endgroup$ – mykhal Nov 8 '18 at 14:02
  • $\begingroup$ @mykhal what is Noise garbage? $\endgroup$ – user67046 Nov 8 '18 at 14:03
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    $\begingroup$ (There's an ugly artificial additional (thus “garbage”) noise because of lossy wavelet transformation (even though quality was set to 90%) at the edges of the graphics in the 1st image, if you ca'nt see that, depends also on monitor technology and settings.) $\endgroup$ – mykhal Nov 8 '18 at 14:12

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