Which one of the following compounds has a lambda_max in its UV-visible spectrum

Question

Which one of the following compounds has a lambda_max in its UV-visible spectrum with the longest wavelength? A) (4E, 7E)-dodeca-1, 4, 7-triene B) (2E, 4E, 6E)-dodeca-2, 4, 6-triene C) (2E, 4E, 10E)-dodeca-2, 4, 10-triene D) (E)-dodeca-1, 5, 11-triene E) (2E, 6E, 8E)-dodeca-2, 6, 8-triene What is the splitting pattern expected for the protons in the molecule CH3CH2-O-CH3? A) singlet B) doublet C) triplet D) quartet E) nonet With the chemical shift defined as the ratio between "distance downfield from the standard in [Hz]" and "operating frequency of the spectrometer in [Hz], " what will be the units of the chemical shift? A) MHz (megahertz) B) Hz (hertz) C) unitless D) KHz (kilohertz) D) ppm (parts per million) Which of the following mass spectral phenomena would indicate the presence of an odd number of nitrogen atoms in a molecule? A) the molecular ion peak had an odd number for its m/z ratio B) the molecular ion peak had an even number for its m/z ratio C) the molecular ion peak is also the base peak D) the molecular ion peak is missing from the spectrum E) none of the above Which isomer of dibenzalacetone has the largest absorptivity? A) E, E B) E, Z C) Z, E D) Z, Z

Explanation / Answer

2. The compound B will have highest lambda max because of highest conjugation present in the molecule. All the double bonds are E isomers and present at alternate positions having single bond in between. This arrangement increases the conjugation. So, answer is B.

3. There are 3 types of proptons present in the molecule, so triplet will be observed. Answer is C.

4. When odd number of N are present in the molecule, then m/z ratio is also odd. So, correct answer is A.

5. Chemical shift is in ppm. So, answer is E.

6. Absorptivity is maximum for Z,Z isomer. Answer is D.

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