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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: jcais on February 09, 2007, 06:03:10 PM

Title: Numbering: Locations of Carbon 6 and 7 on alpha-pinene
Post by: jcais on February 09, 2007, 06:03:10 PM

Hello,

alpha-pinene is named 2,6,6-trimethyl bicyclo[3.1.1]hept-2-ene. Let's ignore the 1s and 5s for now, because I haven't learned that yet. :-)

Does this mean that the carbon between bridgehead 1 and bridgehead 5 is Carbon #6?

Then, this would place Carbon #7 *between* Carbon #1 and Carbon #5. Is this okay?

I thought that the Carbon #7 would be between Carbon #1 and Carbon #5 and that Carbon #6 would go between Carbon #1 and Carbon #5, because I'm numbering counterclockwise along the longest bridge. Why stop short and place Carbon 6 in the middle?

It just seems out of numerical order to name it 2,6,6-trimethyl bicyclo[3.1.1]hept-2-ene. Can anyone explain this to me? Thank you!

Title: Re: Numbering: Locations of Carbon 6 and 7 on alpha-pinene
Post by: movies on February 09, 2007, 06:46:32 PM

Yes, it would be numbered the way you described.  With bicycles you count from the bridgehead around the largest ring and then you skip to the other bridging chains and finally to any substituents.  So really, you count all the way around the six membered ring and then skip to the last remaining carbon; it's not really out of order.