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Topic: H-NMR geminal coupling constants influenced by bond angle  (Read 4912 times)

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Offline zeoblade

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H-NMR geminal coupling constants influenced by bond angle
« on: December 01, 2010, 11:26:35 PM »
H-NMR geminal coupling constants influenced by bond angle

decreasing ring size (except C5 and C6) decreases C-C-C bond angle
increasing ring size (to an extent) also decreases C-C-C bond angle
but does the C-C-H and H-C-H bond angle increase?

a textbook says that as H-C-H bond angle increases from decreasing ring size the geminal coupling constant increases from -ive to +ive
is this correct about the trend in increasing/decreasing ring size increasing/decreasing ring strain increasing/decreasing which bond angle?
would someone be kind enough to confirm the trend?

Offline discodermolide

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Re: H-NMR geminal coupling constants influenced by bond angle
« Reply #1 on: December 02, 2010, 07:52:26 AM »
H-NMR geminal coupling constants influenced by bond angle

decreasing ring size (except C5 and C6) decreases C-C-C bond angle
increasing ring size (to an extent) also decreases C-C-C bond angle
but does the C-C-H and H-C-H bond angle increase?

a textbook says that as H-C-H bond angle increases from decreasing ring size the geminal coupling constant increases from -ive to +ive
is this correct about the trend in increasing/decreasing ring size increasing/decreasing ring strain increasing/decreasing which bond angle?
would someone be kind enough to confirm the trend?

Look up the Karplus equation, you may find something there
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Offline zeoblade

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Re: H-NMR geminal coupling constants influenced by bond angle
« Reply #2 on: December 02, 2010, 09:26:23 PM »
karplus equation relates the vicinal coupling constant to C-C-H angle but I want to know the influence of increasing/decreasing ring size on the H-C-H angle

in geminal coupling the textbook says the coupling constant is affected by the H-C-H angle and I asked about the influence of ring size on H-C-H angle

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