I need help with is ochem question..!

[jungjh9001]

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I'm studying for ochem test tomorrow, and I don't get how they got this answer..
If I have Br,CH3,CH2 and,CH2 attached to a carbon atom, isn't it supposed to be achiral?
(The carbon is part of a pentagon)
If it is chiral, there has to be 4 different substituents, but two of the substituents are same..

 

[hsb1104]

What do you mean the carbon is part of a "pentagon".. do you mean one the carbons is part of a cyclopentane ring? and the 3 other molecules are attached to one carbon on the ring? you need to clarify

 

[jungjh9001]

What do you mean the carbon is part of a "pentagon".. do you mean one the carbons is part of a cyclopentane ring? and the 3 other molecules are attached to one carbon on the ring? you need to clarify

Yes.. that's what I meant to say.. 🙂
It is part of cyclopentane ring, and the two H's on the CH2 are not actually drawn on the picture.

 

[hsb1104]

Are there any double bonds or any other substituents on the ring?

 

[jungjh9001]

Are there any double bonds or any other substituents on the ring?

There are two CH3's attached to one of the other carbons.. (also part of cyclopentane ring)
and there is no double bond..
Thank you for the help!

 

[hsb1104]

K that's why. When the chirality of a carbon in a ring is in question you need to look at the whole ring. Check out the last section on this page (introducing rings - further complications) it explains it really well
http://www.chemguide.co.uk/basicorg/isomerism/optical.html

 

[Pojman]

A substituent will not stop with a CH2 unless there is a double bond. In this molecule, I am thinking that it would be impossible to have a double bond. So - Does the CH2 have anything else attached to it? If the rest of the substituent is the same, then it is achiral. If the rest of the substituent is different, than it is chiral. I guess the moral of this story is, it does not necessarily matter what the chiral carbon is directly attached to, it only matters if the substituent, in its entirety, is different.

When dealing with a ring, you just keep jumping atoms until you either reach a point of symmetry, or you will find a point of difference. If you are having trouble with OChem, I would suggest this website to anyone. http://www.freelance-teacher.com/videos.htm

 

[jungjh9001]

Thank you all for the help!
I think I got it now! 🙂

 

[Nelcovp]

When in doubt, the answer is resonance. =)