all 24 ti For HPLC UV-vis detector, which one (ones) can be detected? (a) hexane

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24 ti For HPLC UV-vis detector, which one (ones) can be detected? (a) hexane (b) chlorobenzene (e) tetrahydrofuran, i.e. THF (d)dichloromethane (e) toluene ; Rationalize your answer (5%) N What is hydrogen bonding? In FTIR spectroscopy, please indicate where the absorption peak of free carbonyl group is located. And where the absorption peak will be located if the hydrogen bonding is present Rationalize your answer. (10%) Please describe the UV-vis absorption characteristics for the following compounds (a) benzene, (b) stilbene, (e) biphenyl, (d) diphenylmethane. Rationalize your answer (10%) Please describe what is Skraup synthesis and its reaction mechanism 10%) +--Under what condition, "crossed Claisen condensation" would be possible. Please give one example for the crossed Claisen condensation reaction. (1096) . Please draw 1H NMR spectrum of methox) cetonitrile. Ratonalize your answer (5%) 2

Explanation / Answer

1) For HPLC UV detector, the ones that have pi-bonds in conjugation will show in UV detector. The ones which fulfil this this criteria is,

b) chlorobenzene, e) toluene

2) Hydrogen bonding is intermolecular attractive force between two groups one of which is hydrogen atom and the other a polar atom such as N, O, etc. The carbonyl group frequency in IR is around 1700 cm-1. When it forms a hydrogen bond the frequency shifts to lower value, like 1680 cm-1.

3) UV-Vis of,

(a) benzene : shows a UV peak at 254 nm. (b) stilbene : with an added double bond, the UV shifts to higher wavelength. (c) biphenyl : shows higher wavelength due to extended conjugation. (d) diphenylmethane : the conjugation breaks here so the uv peak is around same as benzene.

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