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Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: Messi on November 06, 2012, 09:51:42 PM

Title: 1-heptyne...
Post by: Messi on November 06, 2012, 09:51:42 PM

I was looking at 1-heptyne on SDBS...

Why does the hydrogen attached to the triple bond only show up in the ~2 region in the NMR spectrum? This makes me confused!

Link:

http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/IMG.cgi?fname=HSP00932&imgdir=hspW (http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/IMG.cgi?fname=HSP00932&imgdir=hspW)

Title: Re: 1-heptyne...
Post by: discodermolide on November 06, 2012, 11:07:39 PM

Imagine the pi electrons of the triple bond as a cylinder with the hydrogen sticking out of one end. The cylinder of the electron cloud influences the chemical shift of the alkyne proton. This proton sits in the so called shielding zone and therefore the shift appears upfield.

see http://en.wikipedia.org/wiki/Chemical_shift (http://en.wikipedia.org/wiki/Chemical_shift) the section on "Factors affecting chemical shifts"