Question 1

Explain why all protons in a molecule do not absorb rf energy at the same frequency.

Accepted Answer

All nuclei in molecules are surrounded by electron clouds. When a uniform external magnetic field is applied to a molecule, the circulating electron clouds set up tiny local magnetic fields of their own. These local magnetic fields act in opposition to the applied field, so that the effective field actually felt by a nucleus is a bit smaller than the applied field.
B_effective = B_applied − B_local
This effect is termed shielding. Each nucleus is shielded to a slightly different extent, so each unique kind of proton in a molecule resonates at a slightly different frequency and gives rise to a unique NMR signal.

Question 2

The following questions pertain to the display of NMR spectra. Match a term to each description below.
-The calibration standard for 1H and 13C NMR is _____.

Accepted Answer

A) TMS 
B) high-field or upfield side 
C) MHz 
D) delta (δ) 
E) low-field or downfield side
F)chemical shift
G)intensity 
A) TMS 
B) high-field or upfield side 
C) MHz 
D) delta (δ) 
E) low-field or downfield side
F)chemical shift
G)intensity A

Question 3

If the proton attached to C2 in 1,1,2-tribromopropane is coupled with the protons on C1 (J = 3.5 Hz) and C3 (J = 6.8), draw the tree diagram of the C2 proton and predict the splitting pattern.

Accepted Answer

The answer of If the proton attached to C2 in...

Question 4

Refer to the structure of 3-methylbutan-2-one below to answer the following question(s).  
-A compound with the molecular formula C6H4ClBr produces only two doublets in the 1H NMR spectrum.
a)Propose a structure for this compound.
b)How many signals would be present in the 13CNMR for this structure?

Accepted Answer

Question 5

To answer the following questions, consider the data and S1U1P11S1S1P0H NMR spectrum below.
The mass spectrum of this compound shows a molecular ion at m/z = 113, the IR spectrum has characteristic absorptions at 2270 and 1735 cm−S1U1P11S1S1P0, and the S1U1P113S1S1P0C NMR spectrum has five signals.   (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)
-Refer to instructions. How many types of nonequivalent protons are there in this molecule?

Accepted Answer

The answer of To answer the following questions, consider the...

Question 6

How many positive and negative peaks appear in the DEPT-135 and in the DEPT-90 spectrum of 2-methylpentane?

Accepted Answer

A)  DEPT-135: two positive and one negative, DEPT-90: one positive 
B)  DEPT-135: three positive and two negative, DEPT-90: one positive 
C)  DEPT-135: three positive and two negative, DEPT-90: no signals 
D)  DEPT-135: two positive and three negative, DEPT-90: two positive 
A)  DEPT-135: two positive and one negative, DEPT-90: one positive 
B)  DEPT-135: three positive and two negative, DEPT-90: one positive 
C)  DEPT-135: three positive and two negative, DEPT-90: no signals 
D)  DEPT-135: two positive and three negative, DEPT-90: two positive

Question 7

The following questions pertain to the display of NMR spectra. Match a term to each description below.
-When looking at an NMR spectrum the right-hand part of the chart is the _____.

Accepted Answer

A) TMS 
B) high-field or upfield side 
C) MHz 
D) delta (δ) 
E) low-field or downfield side
F)chemical shift
G)intensity 
A) TMS 
B) high-field or upfield side 
C) MHz 
D) delta (δ) 
E) low-field or downfield side
F)chemical shift
G)intensity

Question 8

Refer to the structure of 3-methylbutan-2-one below to answer the following question(s).  
-Treatment of tert-butyl alcohol with hydrogen chloride yields a mixture of tert-butyl chloride and 2-methylpropene.   a)After chromatographic separation, how would you use 1H NMR to help you decide which was which?
b)How would the 13C NMR for the two compounds differ?

Accepted Answer

a)
2-Methylpropene has two kinds of hydr

Question 9

To answer the following questions, consider the data and S1U1P11S1S1P0H NMR spectrum below.
The mass spectrum of this compound shows a molecular ion at m/z = 113, the IR spectrum has characteristic absorptions at 2270 and 1735 cm−S1U1P11S1S1P0, and the S1U1P113S1S1P0C NMR spectrum has five signals.   (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)
-Refer to instructions. Based on the mass spectral data and the IR data, what functional groups are present in this compound?

Accepted Answer

A molecular ion of mass 113 indicates an

Question 10

Which feature in the 1H NMR spectrum provides information about the electronic environment of the protons in a compound?

Accepted Answer

A)  number of signals 
B)  integration of signals 
C)  splitting of signals 
D)  chemical shift 
A)  number of signals 
B)  integration of signals 
C)  splitting of signals 
D)  chemical shift

Question 11

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled S1U1P113S1S1P0C NMR spectra.
-Number of signals:

Accepted Answer

The answer of For each of the compounds below tell...

Question 12

The following questions pertain to the display of NMR spectra. Match a term to each description below.
-The NMR spectrum are calibrated using an arbitrary scale that is divided into _____ units.

Accepted Answer

A) TMS 
B) high-field or upfield side 
C) MHz 
D) delta (δ) 
E) low-field or downfield side
F)chemical shift
G)intensity 
A) TMS 
B) high-field or upfield side 
C) MHz 
D) delta (δ) 
E) low-field or downfield side
F)chemical shift
G)intensity

Question 13

Which of the following would not produce nuclear magnetic resonance?

Accepted Answer

A)  "2H" 
B)  "14N" 
C)  "16O" 
D)  "19F" 
A)  "2H" 
B)  "14N" 
C)  "16O" 
D)  "19F"

Question 14

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled S1U1P113S1S1P0C NMR spectra.
-Number of signals:

Accepted Answer

The answer of For each of the compounds below tell...

Question 15

Refer to the structure of 3-methylbutan-2-one below to answer the following question(s).  
-Refer to instructions. What is the ratio of peak areas upon integration of the spectrum for A, B, and C respectively?

Accepted Answer

A)  3:1:3:3 
B)  1:1:6 
C)  1:1:6.0 
D)  3:1:6 
A)  3:1:3:3 
B)  1:1:6 
C)  1:1:6.0 
D)  3:1:6

Question 16

Which of the following compounds gives a 1H NMR spectrum consisting of only a singlet and two signals in the 13C NMR?

Accepted Answer

A)  1,1-dibromopropane 
B)  1,2-dibromopropane 
C)  1,3-dibromopropane 
D)  2,2-dibromopropane 
A)  1,1-dibromopropane 
B)  1,2-dibromopropane 
C)  1,3-dibromopropane 
D)  2,2-dibromopropane

Question 17

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled S1U1P113S1S1P0C NMR spectra.
-Number of signals:

Accepted Answer

The answer of For each of the compounds below tell...

Question 18

Which structure of molecular formula C4H8Cl2 fits the 1H NMR and 13C NMR spectra shown below?     (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)

Accepted Answer

A) 
  
B) 
  
C) 
  
D) 
  
A) 
  
B) 
  
C) 
  
D)

Question 19

Which feature in the 1H NMR spectrum provides information about the relative numbers of hydrogen atoms of each type found in a compound?

Accepted Answer

A)  number of signals 
B)  integration of signals 
C)  splitting of signals 
D)  chemical shift 
A)  number of signals 
B)  integration of signals 
C)  splitting of signals 
D)  chemical shift

Question 20

Which feature in the 1H NMR spectrum provides information about the number of neighboring protons of each proton in the compound?

Accepted Answer

A)  number of signals 
B)  integration of signals 
C)  splitting of signals 
D)  chemical shift 
A)  number of signals 
B)  integration of signals 
C)  splitting of signals 
D)  chemical shift

Exam 11: Structure Determination: Nuclear Magnetic Resonance Spectroscopy

Explain why all protons in a molecule do not absorb rf energy at the same frequency.

The following questions pertain to the display of NMR spectra. Match a term to each description below. -The calibration standard for 1H and 13C NMR is _____.

If the proton attached to C2 in 1,1,2-tribromopropane is coupled with the protons on C1 (J = 3.5 Hz) and C3 (J = 6.8), draw the tree diagram of the C2 proton and predict the splitting pattern.

Refer to the structure of 3-methylbutan-2-one below to answer the following question(s). -A compound with the molecular formula C6H4ClBr produces only two doublets in the 1H NMR spectrum. a)Propose a structure for this compound. b)How many signals would be present in the 13CNMR for this structure?

How many positive and negative peaks appear in the DEPT-135 and in the DEPT-90 spectrum of 2-methylpentane?

The following questions pertain to the display of NMR spectra. Match a term to each description below. -When looking at an NMR spectrum the right-hand part of the chart is the _____.

Which feature in the 1H NMR spectrum provides information about the electronic environment of the protons in a compound?

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled 13C NMR spectra. -Number of signals:

The following questions pertain to the display of NMR spectra. Match a term to each description below. -The NMR spectrum are calibrated using an arbitrary scale that is divided into _____ units.

Which of the following would not produce nuclear magnetic resonance?

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled 13C NMR spectra. -Number of signals:

Refer to the structure of 3-methylbutan-2-one below to answer the following question(s). -Refer to instructions. What is the ratio of peak areas upon integration of the spectrum for A, B, and C respectively?

Which of the following compounds gives a 1H NMR spectrum consisting of only a singlet and two signals in the 13C NMR?

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled 13C NMR spectra. -Number of signals:

Which structure of molecular formula C4H8Cl2 fits the 1H NMR and 13C NMR spectra shown below? (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)

Which feature in the 1H NMR spectrum provides information about the relative numbers of hydrogen atoms of each type found in a compound?

Which feature in the 1H NMR spectrum provides information about the number of neighboring protons of each proton in the compound?

Structure and Bonding

Polar Covalent Bonds; Acids and Bases

Organic Compounds: Alkanes and Their Stereochemistry

Organic Compounds: Cycloalkanes and Their Stereochemistry

Stereochemistry at Tetrahedral Centers

An Overview of Organic Reactions

Alkenes and Alkynes

Reactions of Alkenes and Alkynes

Aromatic Compounds

Structure Determination: Mass Spectrometry, Infrared Spectroscopy, and Ultraviolet Spectroscopy

Structure Determination: Mass Spectrometry, Infrared Spectroscopy, and Ultraviolet Spectroscopy

Organohalides: Nucleophilic Substitutions and Eliminations

Alcohols, Phenols, and Thiols; Ethers and Sulfides

Aldehydes and Ketones: Nucleophilic Addition Reactions

Carboxylic Acids and Nitriles

Carboxylic Acid Derivatives: Nucleophilic Acyl Substitution Reactions

Carbonyl Alpha-Substitution and Condensation Reactions

Amines and Heterocycles

Biomolecules: Amino Acids, Peptides, and Proteins

Amino Acid Metabolism

Biomolecules: Carbohydrates

Carbohydrate Metabolism

Biomolecules: Lipids and Their Metabolism

Biomolecules: Nucleic Acids and Their Metabolism

Orbitals and Organic Chemistry: Pericyclic Reactionse

Synthetic Polymerse

Filters

The following questions pertain to the display of NMR spectra. Match a term to each description below. -The calibration standard for ¹H and ¹³C NMR is _____.

Which feature in the ¹H NMR spectrum provides information about the electronic environment of the protons in a compound?

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra. -Number of signals:

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra. -Number of signals:

Which of the following compounds gives a ¹H NMR spectrum consisting of only a singlet and two signals in the ¹³C NMR?

For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra. -Number of signals:

Which structure of molecular formula C₄H₈Cl₂ fits the ¹H NMR and ¹³C NMR spectra shown below? (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)

Which feature in the ¹H NMR spectrum provides information about the relative numbers of hydrogen atoms of each type found in a compound?

Which feature in the ¹H NMR spectrum provides information about the number of neighboring protons of each proton in the compound?