Question 1

Any process faster than ________ will be recorded as an average by NMR spectroscopy.

Accepted Answer

The T2 relaxation time, which determines the ability to distinguish between different chemical environments, is typically on the order of milliseconds. Any process faster than 0.01 seconds will be recorded as an average by NMR spectroscopy. Therefore, option C, 0.01 seconds, is the best choice.

Question 2

Predict the number of signals expected in the proton spin decoupled ¹³C spectrum of cyclopentane.

Accepted Answer

The answer of Predict the number of signals expected in...

Question 3

The ¹H NMR spectrum of ethanol is acquired and the hydroxyl signal appears as a singlet instead of a triplet. Offer an explanation.

Accepted Answer

The answer of The ¹H NMR spectrum of ethanol is...

Question 4

What type of carbon environment does not generate a signal in the DEPT-90 spectrum and gives a negative signal in the DEPT-135 spectrum?

Accepted Answer

The answer of What type of carbon environment does not...

Question 5

What is the approximate chemical shift of an alkynyl carbon in ¹³C NMR spectroscopy?

Accepted Answer

The chemical shift of an alkynyl carbon typically falls in the range of 60-90 ppm in NMR spectroscopy. Choosing the closest option, the answer would be approximately 70 ppm.

Question 6

What type of carbon environment does not generate a signal in the DEPT-90 spectrum and gives a positive peak in the DEPT-135 spectrum?

Accepted Answer

The answer of What type of carbon environment does not...

Question 7

What compound exhibits three singlets in its proton spin decoupled ¹³C NMR spectrum?

Accepted Answer

The answer of What compound exhibits three singlets in its...

Question 8

How many peaks appear in the proton spin decoupled ¹³C NMR spectrum of the compound below?

Accepted Answer

The answer of How many peaks appear in the proton...

Question 9

You have a sample and its ¹H NMR spectrum. You know your sample contains O atoms but not N atoms, and you suspect that your sample may be an alcohol. What common spectroscopic technique might you use to confirm your suspicion?

Accepted Answer

The answer of You have a sample and its ¹H...

Question 10

Explain the difference between off-resonance decoupling and broadband decoupling and how each affects the C-13 NMR spectrum. In your discussion include a short description of how a chemist interprets the different spectra.

Accepted Answer

The answer of Explain the difference between off-resonance decoupling and...

Question 11

An NMR spectrometer that operates at a frequency of 60 MHz for ¹³C NMR spectra, operates at what frequency for ¹H NMR spectra?

Accepted Answer

The answer of An NMR spectrometer that operates at a...

Question 12

Predict the number of signals expected in the proton spin decoupled ¹³C NMR spectrum of the compound shown below.

Accepted Answer

The answer of Predict the number of signals expected in...

Question 13

How might the proton spectrum of ultrapure dimethylamine, (CH₃)₂NH, differ from the spectrum of this compound to which D₂O has been added?

Accepted Answer

The answer of How might the proton spectrum of ultrapure...

Question 14

What multiplicities are observed in the off-resonance decoupled ¹³C spectrum of 2,3-dimethyl-but-2-ene?

Accepted Answer

The answer of What multiplicities are observed in the off-resonance...

Question 15

How many peaks appear in the proton spin decoupled ¹³C NMR spectrum of the compound below?

Accepted Answer

The answer of How many peaks appear in the proton...

Question 16

Give one reason why ¹³C NMR is less sensitive than ¹H NMR.

Accepted Answer

The answer of Give one reason why ¹³C NMR is...

Question 17

Why is carbon-carbon splitting typically not seen in ¹³C NMR spectra?

Accepted Answer

The answer of Why is carbon-carbon splitting typically not seen...

Question 18

If a signal is observed in the 170 to 200 ppm range in a C-13 NMR spectrum, what is the most likely type of functional group associated with that carbon atom?

Accepted Answer

The 170 to 200 ppm range in a C-13 NMR spectrum is characteristic of carbonyl carbons, which are typically found in aldehydes, ketones, carboxylic acids, and esters.

Question 19

Which compound generates positive peaks for the carbonyl in both its DEPT-90 and DEPT-135 spectra?

Accepted Answer

The answer of Which compound generates positive peaks for the...

Question 20

The chair form of cyclohexane has protons in two distinct environments, axial and equatorial. When the proton NMR of cyclohexane is run on a 100-MHz instrument at 23°C, only one signal for the compound is observed. Explain this apparent contradiction.

Accepted Answer

The answer of The chair form of cyclohexane has protons...

Quiz 13: Nuclear Magnetic Resonance Spectroscopy

Any process faster than ________ will be recorded as an average by NMR spectroscopy.

Predict the number of signals expected in the proton spin decoupled 13C spectrum of cyclopentane.

The 1H NMR spectrum of ethanol is acquired and the hydroxyl signal appears as a singlet instead of a triplet. Offer an explanation.

What type of carbon environment does not generate a signal in the DEPT-90 spectrum and gives a negative signal in the DEPT-135 spectrum?

What is the approximate chemical shift of an alkynyl carbon in 13C NMR spectroscopy?

What type of carbon environment does not generate a signal in the DEPT-90 spectrum and gives a positive peak in the DEPT-135 spectrum?

What compound exhibits three singlets in its proton spin decoupled 13C NMR spectrum?

How many peaks appear in the proton spin decoupled 13 C NMR spectrum of the compound below?

You have a sample and its 1H NMR spectrum. You know your sample contains O atoms but not N atoms, and you suspect that your sample may be an alcohol. What common spectroscopic technique might you use to confirm your suspicion?

Explain the difference between off-resonance decoupling and broadband decoupling and how each affects the C-13 NMR spectrum. In your discussion include a short description of how a chemist interprets the different spectra.

An NMR spectrometer that operates at a frequency of 60 MHz for 13C NMR spectra, operates at what frequency for 1H NMR spectra?

Predict the number of signals expected in the proton spin decoupled 13C NMR spectrum of the compound shown below.

How might the proton spectrum of ultrapure dimethylamine, (CH3)2NH, differ from the spectrum of this compound to which D2O has been added?

What multiplicities are observed in the off-resonance decoupled 13C spectrum of 2,3-dimethyl-but-2-ene?

How many peaks appear in the proton spin decoupled 13 C NMR spectrum of the compound below?

Give one reason why 13C NMR is less sensitive than 1H NMR.

Why is carbon-carbon splitting typically not seen in 13C NMR spectra?

If a signal is observed in the 170 to 200 ppm range in a C-13 NMR spectrum, what is the most likely type of functional group associated with that carbon atom?

Which compound generates positive peaks for the carbonyl in both its DEPT-90 and DEPT-135 spectra?

The chair form of cyclohexane has protons in two distinct environments, axial and equatorial. When the proton NMR of cyclohexane is run on a 100-MHz instrument at 23°C, only one signal for the compound is observed. Explain this apparent contradiction.

Predict the number of signals expected in the proton spin decoupled ¹³C spectrum of cyclopentane.

The ¹H NMR spectrum of ethanol is acquired and the hydroxyl signal appears as a singlet instead of a triplet. Offer an explanation.

What is the approximate chemical shift of an alkynyl carbon in ¹³C NMR spectroscopy?

What compound exhibits three singlets in its proton spin decoupled ¹³C NMR spectrum?

How many peaks appear in the proton spin decoupled ¹³C NMR spectrum of the compound below?

You have a sample and its ¹H NMR spectrum. You know your sample contains O atoms but not N atoms, and you suspect that your sample may be an alcohol. What common spectroscopic technique might you use to confirm your suspicion?

An NMR spectrometer that operates at a frequency of 60 MHz for ¹³C NMR spectra, operates at what frequency for ¹H NMR spectra?

Predict the number of signals expected in the proton spin decoupled ¹³C NMR spectrum of the compound shown below.

How might the proton spectrum of ultrapure dimethylamine, (CH₃)₂NH, differ from the spectrum of this compound to which D₂O has been added?

What multiplicities are observed in the off-resonance decoupled ¹³C spectrum of 2,3-dimethyl-but-2-ene?

How many peaks appear in the proton spin decoupled ¹³C NMR spectrum of the compound below?

Give one reason why ¹³C NMR is less sensitive than ¹H NMR.

Why is carbon-carbon splitting typically not seen in ¹³C NMR spectra?