Describe and explain the possible effect on your results of the following experi

Question

Describe and explain the possible effect on your results of the following experimental or conceptual errors. The infrared chart paper on a dispersive IR spectrometer wasn't aligned correctly when you recorded your spectrum. One of your compounds was 3, 7-dimethyl-2.6-octadienal. In writing its structure, you inadvertently put the #2 double bond between the #3 and #4 carbon atoms. In comparing an aldehyde and a ketone, you assumed that an alkyl group is electron withdrawing relative to hydrogen, because in general chemistry you learned that carbon is more electronegative than hydrogen.

Explanation / Answer

2

a) A non aligned chart paper is not a major problem, as non alignment only mess up the base line of the recorded spectrum. Otherwise the spectrum is not cut out due to huge non alignment is almost similar to the properly paper aligned printed spectrum.

b) It is a well known fact that conjugation moves the C=O stretching frequencies to lower wave number in the structure of 3,7-dimethyl-2,6-octadienal the aldehyde is in conjugation with the double bond at the 2 position if you write the double bond at the 3 position you will expect the double bond of the aldehyde to appear at arounf 1720 - 1750 cm-1 whereas in the actual compound it will appear at around 1680 cm-1 due to the conjugation.

3) The expected shift for a C=O stretching frquency on substituting with an electronwithdrawing group is a shift towards higher wave numbers. On the other hand presnec of electron donating group shift the C=O stretching towards lower wavenumbers. If you assume the alkyl to be electron withdraawing you will expect the shift to appear at higher wavenumber but the actual shift will be towards lower wavenumber.

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