Tell how UV-Vis spectrometry you can compounds. Calculate approximate values for

Question

Tell how UV-Vis spectrometry you can compounds. Calculate approximate values for each compound when you can. 1,4-hexadiene. 2.4-hexadiene. and 1.3-hexadiene cyclohexanone. 2-cyclohexenone, and 2.4-cyclohexadienone the following compounds Tell how 'H-NMR can be ued to differentiate the following compounds. In each case describe the characteristic multiplets and coupling which can be expected for each compound. 1-butanol. 2-butanol, and 2-methy1-2-butanol butanal. 1-butanol. 2-butanone cyclohexanone. 2-cyclohexenone Classify each of the following (as a monoterponotd, sesquiterpenoid. etc.) and show how each can be divided into isoprene units. TeII how you could use a spectrometric method to distinguish geraniol (see Figure 2) from neral.

Explanation / Answer

3. Identification based on UV-Vis spectroscopy

(a) 1,4-hexadiene is a non-conjugates diene. 2,4-hexadiene and 1,3-hexadiene are conjugated internal and external diene systems.

calculation of lambda-max

1,4-hexadiene = non-conjugated, not needed

2,4-hexadiene = 214 + 2 x 5 = 224 nm

1,3-hexadiene = 214 + 5 = 217 nm

So, as can be seen, 2,4-hexadiene will absorb at hgihest value than 1,3-hexadiene and least absorption will be seen for non-conjugated 1,4-hexadiene system.

(b) cyclohexanone is a ketone, 2-cyclohexenone is a enone and 2,4-cyclohexadienone is a extended conjugated enone system

calculating lambda-max values

cyclohexanone = non-conjugated, not required

2-cyclohexenone = 215 + 12 = 227 nm

2,4-cyclohexadienone = 215 + 18 + 30 + 39 = 302 nm

So as can be seen, a ketone absorbs at lowest wavelength, followed by conjugated enone and highest would be for dienone system.

(c) 1 is an homoannular diene with lambda-max = 253 + 2 x 5 = 263 nm

2 is an homannular tetrasubstituted diene, lambda-max = 253 + 4 x 5 = 273 nm

3 is an heteroannular diene, lambda-max = 214 + 4 x 5 + 2 x 5 = 244 nm

So as can be seen 1 would give maximum lambda-max and 3 would give lowest lambda-max absorption.

4. Analysis by 1H NMR

(a) 1-butanol would have a triplet for 2H at 3.7 ppm for CH2 next to -OH

2-butanol would have a sextet for 1H at 3.8 ppm for CH next to -OH

2-methyl-2-butanol would have no peaks in the 3-4 ppm region, but will have 1 singlet for 6H at 1.2 ppm for 2 CH3's

(b) Butanal will have a singlet at 10 ppm for aldehydic CH proton

1-butanol will not have any peaks in 8-10 region, but will have triplet at 3.7 for CH2 protons next to -OH

2-butanone will have a singlet at 2.1 ppm for CH3 next to C=O

(c) cyclohexanone will have a triplet for 4H, a quintet for 4H and a quintet for 2H in spectrum

2-cyclohexenone will have a doublet at 5.4 ppm for alkenic CH, a triplet at 5.7 ppm for CH at beta-position of olefin and doublet of triplet for CH2 next to alkene carbon

5. Linalool is a diterpenoid

Caryophylliene is a sesquiterpenoid

beta-selinene is a sesquiterpenoid

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