Organic Chemistry Questions and Answers – UV – Visible Spectroscopy

1 What is the wavelength range for UV spectrum of light?

A 400 nm – 700 nm

B 700 nm to 1 mm

C 0.01 nm to 10 nm

D 10 nm to 400 nm

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Answer: 10 nm to 400 nm

2 Which of the following comparison is correct for solvent shift on the n –>π* transition of acetone?

A H₂0 = CH₃0H = C₂H₅0H = CHC1₃ = C₆H₁₄

B H₂0 > CH₃0H > C₂H₅0H > CHC1₃ > C₆H₁₄

C H₂0 < CH₃0H < C₂H₅0H < CHC1₃ < C₆H₁₄

D H₂0 > CH₃0H < C₂H₅0H < CHC1₃ < C₆H₁₄

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Answer: H₂0 < CH₃0H < C₂H₅0H < CHC1₃ < C₆H₁₄

3 What is the correct order of λmax for n –> σ* transition?

A R-OH > R-NH₂ > R-SH

B R-OH < R-NH₂ < R-SH

C R-OH > R-SH > R-NH₂

D R-OH < R-SH < R-NH₂

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Answer: R-OH < R-NH₂ < R-SH

4 What is the correct order of λ_max for n –> π* transition for the R-CN, R-NO₂, and R-N=N-R?

A R-CN < R-NO₂ < R-N=N-R

B R-CN = R-NO₂ = R-N=N-R

C R-CN > R-NO₂ > R-N=N-R

D R-CN > R-NO₂ < R-N=N-R

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Answer: R-CN < R-NO₂ < R-N=N-R

5 What is the correct order of λ_max for π –> π* transition for the following three compounds?

A R-C=C-R > R₂C = CR₂ > R-CHO

B R-C=C-R < R₂C = CR₂ < R-CHO

C R-C=C-R = R₂C = CR₂ = R-CHO

D R-C=C-R < R₂C = CR₂ >R-CHO

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Answer: R-C=C-R < R₂C = CR₂ < R-CHO

6 What is the correct order of λ_max for n–> π* transition for the following three compounds?

A RCOOH > RCOOR’ > RCONH₂

B RCOOH = RCOOR’ = RCONH₂

C RCOOH = RCOOR’ < RCONH₂

D RCOOH = RCOOR’ > RCONH₂

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Answer: RCOOH = RCOOR’ = RCONH₂

7 Which of the following is the correct order of λ_max for n–> π* transition for the given compounds?

Organic Chemistry

A 1>2>3>4>5

B 1<2<3<4<5

C 1>2<3>4<5

D 1>2>3<4>5

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Answer: 1>2>3>4>5

8 The ultraviolet spectrum of benzonitrile shows a primary absorption band at 224 nm. If a solution of benzonitrile in water, with a concentration of 1x 10^-4 molar, is examined at a wavelength of 224 nm, the absorbance is determined to be 1.30. The cell length is 1 cm. What is the molar absorptivity of this absorption band?

A 2.3 x 10⁴

B 3.3 x 10⁴

C 1.3 x 10⁴

D 4.3 x 10⁴

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Answer: 1.3 x 10⁴

9 The ultraviolet spectrum of benzonitrile shows a secondary absorption band at 271 nm. If a solution of benzonitrile in water, with a concentration of 1×10^-4 molar solution is examined at 271 nm, what will be the absorbance reading ( ɛ = 1000) and what will be the intensity ratio, IO/I, respectively?

A 0.1, 1.26

B 0.2, 2.26

C 0.3, 3.26

D 0.4, 4.26

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