Question

What do you notice about the frequency of the C-H stretch as you go from hexane to 1-hexene to 1-hexyne?

What factors do you think can contribute to this difference in C-H stretching frequency?

Answer 1

we can model bonds as springs, how does the frequency of oscillation of a spring change with increasing "stiffness"?

Answer 2

maybe the word stretch is not appropriate
but the relative bond length do changes from singe to double and triple bonds

Answer 3

the word stretch is used in IR spectroscopy - which is what this is about.

Answer 4

Yeah @aaronq I think they do talk about bond stretching in IR a lot.. as you go from single to double to triple the number of bonds increases and bond length goes down.

But i'm not sure though I mean I guess that if bond length goes down that would affect the frequency of oscillations, maybe fewer. perhaps since double and triple bonds have fewer degrees of freedom.

Answer 5

bond length shortening increases the frequency of oscillations

Answer 6

Yes, stretching is an appropriate word.