CH Absorption Bands in Infrared Spectroscopy

[@amidfallen]

Interesting is, that on IR spectra, the SP hybridized C-H bond has higher wavenumber than SP2 C-H. So if I am correct, the bond C-H in ethyne is stronger than in ethene. But, if you compare acidic character, ethyne is stronger acid than ethene, so that would mean, that ethyne has (from acidobazic point of view) weaker C-H bond. Did I missed something?

[@drtriyuginarayanojha8112]

The C-H bond in ethyne is a bit polar and stretching a polar bond requires more energy because you have to pull apart oppositely charged atoms. In alkane this bond is almost nonpolar, so easier to stretch.

[@MaxMax-tt6db]

@@drtriyuginarayanojha8112 Oh so the polarity helps with giving off the proton, but limits it´s movement when still attached? Thanks for explaining this

[@drtriyuginarayanojha8112]

Excellent

[@calebhan7560]

For @8.20 Since aldehyde hydrogen is bonded to sp2 hybridised carbon, shouldnt the peak be to the left of 3000

[@christinecaseres189]

While I agree that if you consider sp2 hybridization, the C-H for an aldehyde hydrogen should be left of 3000, but that isn't the case. There is an important doublet band for an aldehyde C-H where one peak is at 2860-2800 cm-1 and the second is at 2760- 2700 cm-1. This doublet allows aldehydes to be distinguished from other carbonyl-containing compounds. In the 4th edition of Introduction to Spectroscopy by Donald Pavai et al., this is explained (p. 58) by Fermi resonance (p. 19). Fermi resonance is when a fundamental vibration couples with an overtone or combination band. I don't really understand it well, but what is presented in the video is correct, just not explained. The lower frequency 2760-2700 cm-1 is often easier to see because it is present in a region where other C-H absorptions peaks are absent.

[@youssramouhssine99]

Thank you

[@taifali1483]

in 7:18 min i think sp2 is in the right not sp3 becuz sp3 3300 cm so more to the left

[@Knowbee]

Hi Taif! Thank you for your comment. I am not quite sure what your question is or what you're trying to clarify. If you could clarify your question, I will do my best to help you. If you're confused about where the absorption bands should be, google: IR Spec EthylBenzene and you will see other sample IR specs of this molecule with the absorption bands identified. Let me know if there is anything else I can do for you.

[@taifali1483]

Yeah i was confused about that section but i get it

[@taifali1483]

Thanx alot for these videos so helpful

[@mustafaalhayali5506]

wrong>>>sp3 is slightly to right of 3000 >>so the video is right

[@manishajain1078]

Sp2 should be on the rite of sp3