Problem 1
Electronic spectra are often reported in terms of wavelength but can also be recorded in wavenumbers. Convert the following absorption maxima given in \(\mathrm{cm}^{-1}\) into \(\lambda\) given in \(\mathrm{nm}:(\mathrm{a})\) \(22700 \mathrm{cm}^{-1}\) \(^{1} ;(b) 35000 \mathrm{cm}^{-1}\)
Problem 2
Normal laboratory UV-VIS spectrometers operate in the range \(\approx 200-900 \mathrm{nm} .\) Which of the following types of electromagnetic radiation does this range cover: (a) visible light; (b) near-UV radiation; (c) vacuum-UV radiation?
Problem 3
Do absorptions in the vacuum-UV involve transitions in which \(\Delta E\) (change in energy) is greater or smaller than those observed in the visible region?
Problem 7
Lycopene \(\left(\lambda_{\max }=469 \mathrm{nm}\right)\) is present in ripe tomatoes. What colour of light does lycopene absorb?
Problem 8
Suggest which types of transitions \(\left(\sigma^{*}+\sigma\right.\) \(\pi^{*}+\pi, \sigma^{*} \prec n\) or \(\pi^{*}+n\) ) give rise to significant features in the electronic spectra of (a) pentane (13.15) (b) pent-l-ene (13.16), (c) octa- 2,4,6 -triene (13.17) and \((d)\) ethanol (13.18)
Problem 9
(a) What is a 'red shift'? (b) Suggest why the methoxy (MeO) substituent in the compound \(\mathrm{MeOCH}=\mathrm{CHCH}=\mathrm{CH}_{2}\) causes a red shift in the UV-VIS spectrum with respect to the spectrum of \(\mathrm{CH}_{2}=\mathrm{CHCH}=\mathrm{CH}_{2}\)
