CH Absorption Bands in Infrared Spectroscopy 

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.

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

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.

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.

Yeah i was confused about that section but i get it

Thanx alot for these videos so helpful

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

Sp2 should be on the rite of sp3