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# 急ar!!plz About the IR calculation frequency and wavenumber

Calculate approximate frequency and wavenumber of the C-H stretching

vibration knowing that the force constant of C-H bond k = 500 N m-1. To

which part of the electromagnetic spectrum would this frequency belong?

Note that carbon atom is much heavier than hydrogen atom.

v= 1/2π √(k/m eff)

(h = 6.626 x 10-34 J s; c = 2.998 x 108 m s-1; NA = 6.022 x 1023 mol-1)

Thank you very much

### 1 Answer

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- 魏王將張遼Lv 71 decade agoFavorite Answer
Since the carbon atom is much heavier than hydrogen atom, meff can be approximated as the mass of a single H atom = 1.66 x 10-27 kg.

Hence v = (1/2π) √(500/1.66 x 10-27) = 8.733 x 1013 Hz

And the wavelength is:

c/v = 2.998 x 108/8.733 x 1013

= 3.433 x 10-6 m or 3.433 x 10-4 cm

Finally the wavenumber is 1/3.433 x 10-4 = 2913 cm-1.

Source(s): My chemical knowledge

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