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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: jena on March 13, 2005, 08:54:12 PM

Title: Prefixes for cycloalkanes
Post by: jena on March 13, 2005, 08:54:12 PM: Hi,

My classmates and I kept going over this question and were stumped about the what the answer was. The question states:

8-methylbicyclo[3.2.1]octane never needs the prefixes?

a. cis or trans
b. endo or exo
c. syn or anti
d. needs all a-c
e. does not need a-c

My answer: b.

but one of my classmates said that it didn't need cis or trans either.

So would this answer be e. does not need a-c.

Please help and Thank You :)
Title: Re:Prefixes for cycloalkanes
Post by: dexangeles on March 13, 2005, 11:47:22 PM: well..

1. what does cis and trans mean? hint: location

2. what does endo and exo stand for? hint: + or -

3. what does syn and anti refer to? hint: addition location

by the way, I believe your E is the correct answer as you stated in the end
Title: Re:Prefixes for cycloalkanes
Post by: movies on March 14, 2005, 01:49:17 PM: Yeah, I agree with e too.

There are no alkenes to have cis/trans, not enough stereocenters to have endo/exo, and since it's locked in the bicycle syn/anti mean nothing.
Title: Re:Prefixes for cycloalkanes
Post by: jena on March 16, 2005, 11:55:55 AM: Hi,

Just thought you should know the answer end up being b., but thank you for your help most of our class was sttumped by this one.

ThankYou :)
Title: Re:Prefixes for cycloalkanes
Post by: dexangeles on March 16, 2005, 04:34:14 PM: you are right, in cyclo hydrocarbons cis and trans are used
why I didn't think of that is my bad, sorry

but do you have the explanation for anti and syn? ???
Title: Re:Prefixes for cycloalkanes
Post by: movies on March 16, 2005, 04:37:55 PM: Quote from: Ad Majorem Dei Gloriam on March 16, 2005, 04:34:14 PM
you are right, in cyclo hydrocarbons cis and trans are used
why I didn't think of that is my bad, sorry

This is weird, cis and trans are sometimes used for cycloalkanes, but very rarely for bicyclics.
Title: Re:Prefixes for cycloalkanes
Post by: jena on March 16, 2005, 11:02:21 PM: Hi,

Remember the question asked which one you can't use. You can use syn and anti for this structure because the 8-methyl is attached to the bridge, if it wasn't attached the bridge then you could use, endo or exo to help figure the name for the structure. Also wouldn't cis and trans come in handy if you use endo or exo. Again I really appreciated everyone's help.

Thank You :)
Title: Re:Prefixes for cycloalkanes
Post by: movies on March 18, 2005, 01:03:00 PM: Okay, but if I called it syn-8-methylbicyclo[3.2.1]cyclooctane how do you tell what the methyl group is syn to? Is there some convention I don't know about? The same for cis and trans.

Is the endo/exo determined based on the larger ring being higher priority? So then if the methyl points over the 3 carbon side of the bicycle then the compound is endo?
Title: Re:Prefixes for cycloalkanes
Post by: jena on March 20, 2005, 09:39:32 PM: Hi,

I thought you could tell if something was syn if it was on the bridge and was pointing to the largest group while anti does the opposite and points to the lowest group. That's what our professor taught us.

Thank You :)
Title: Re:Prefixes for cycloalkanes
Post by: movies on March 21, 2005, 12:49:50 AM: Quote from: jena on March 20, 2005, 09:39:32 PM
I thought you could tell if something was syn if it was on the bridge and was pointing to the largest group while anti does the opposite and points to the lowest group. That's what our professor taught us.

So it would be syn if the methyl were pointing toward the 3 carbon linker and anti if it were pointing to the 2 carbon linker in your example?

It's been over three years since I took the class that taught about the naming of bicycles!
Title: Re:Prefixes for cycloalkanes
Post by: jena on March 21, 2005, 02:06:50 PM: Hi,

Yes I believe based off what my professor taught me, that is the correct method.

Thank You :)