Question 1

Which compound contains two three-proton singlets in its NMR spectrum?

Accepted Answer

A)  compound a 
B)  compound b 
C)  compound c 
D)  compound d 
A)  compound a 
B)  compound b 
C)  compound c 
D)  compound d C

Question 2

Deduce the structure of the unknown compound C6H12O, whose IR and NMR spectra are shown. Explain how you arrived at your structure.
 $\mathrm { C } _ { 6 } \mathrm { H } _ { 12 } \mathrm { O }$
  ​

Accepted Answer

First calculate the degree of unsaturation from the molecular formula. Recall the formula: $$U = \frac { 2 C + 2 - H } { 2 }$$ The unsaturation number is equal to (2*6+2-12)/2 = 1, so there is at least one double bond or ring. The IR spectrum shows a diagnostic peak for hydroxy, but not much else. The NMR spectra confirms the presence of the hydroxy group with a peak at 2.0 ppm that disappears after a D₂O shake. The NMR spectra also show two inequivalent methyl groups, two CH₂ groups and an alkene proton. Since there is only one alkene proton, the unknown compound must be a trisubstituted alkene. The chemical shift of the CH₂ group at 3.6 ppm suggests it is near the hydroxy group, giving the fragment -CH₂OH. Putting the fragments together, the structure must be: Let's check the structure and make sure it matches the data. The two methyl groups are diastereotopic, so they will not be equivalent. They do not have any adjacent protons, so they are singlets. The CH₂ group bonded to the alkene is split by the alkene proton and the adjacent methylene to give an apparent quartet. The alkene is split by the CH₂ group, but also by some long-range coupling interactions by protons transmitted by the pi electrons. The remaining CH₂ group is expected to be a triplet and the hydroxy proton is a singlet, as expected.

Question 3

Consider the compound.
   a. How many separate singlets (unsplit NMR resonances) are there in the NMR spectrum of this compound?
b. The resonance that is at the highest frequency (farthest to the left) is
1. a.
2. b.
3. c.
4. d and/or e.
5. f.
c. The resonance of protons c appears as
1. a singlet.
2. a doublet.
3. a triplet.
4. a very complex pattern because the protons are diastereotopic.

Accepted Answer

a. There are three singlets; protons d and e are equivalent. Thus, protons a, d + e, and f are the three singlets.
b. The candidates would be a, d, e, and b because these protons are closest to an oxygen. Because methylene protons have a greater chemical shift than methyl protons with the same adjacent atom, the answer is b.
c. Protons c appear as a triplet. (They are enantiotopic and thus equivalent; they are adjacent to two protons, for which the n + 1 rule gives a triplet.)

Question 4

Deduce a structure that corresponds to the molecular formula and NMR spectra. Explain how you arrived at this structure.
​
Molecular formula: C5H12O.
1H NMR: F1F1F1S1F1F1F10 1.18 (3H, t, J = 8 Hz); F1F1F1S1F1F1F10 1.13 (6H, d, J = 6.8 Hz); F1F1F1S1F1F1F10 3.53 (2H, q, J = 8.0 Hz); F1F1F1S1F1F1F10 3.65 (1H, septet, J = 6.8 Hz).

Accepted Answer

First calculate the degree of unsaturati

Question 5

In an NMR spectrometer operating at ν0 = 300 MHz, a resonance that has a chemical shift of 2.0 ppm (i.e., F1F1F1S1F1F1F10 2) occurs at a frequency that is

Accepted Answer

A)  600 Hz greater than the absorption frequency of the standard TMS. 
B)  600 × 106 Hz greater than the absorption frequency of TMS 
C)  150 Hz greater than the absorption frequency of TMS. 
D)  150,000,000 Hz greater than the absorption frequency of TMS. 
E)  302 Hz greater than the absorption frequency of TMS.f. 
less than the absorption frequency of TMS. 
A)  600 Hz greater than the absorption frequency of the standard TMS. 
B)  600 × 106 Hz greater than the absorption frequency of TMS 
C)  150 Hz greater than the absorption frequency of TMS. 
D)  150,000,000 Hz greater than the absorption frequency of TMS. 
E)  302 Hz greater than the absorption frequency of TMS.f. 
less than the absorption frequency of TMS.

Question 6

What radiation frequency (in sec-1, or Hz) is required to bring a set of protons into resonance if they experience a magnetic field of 50,000 gauss? Show your work.

Accepted Answer

The frequency is pro

Question 7

7. Consider the NMR spectrum of the compound:
  
-The protons labeled ________________.

Accepted Answer

A)  should have the smallest chemical shift in the spectrum 
B)  should have the greatest chemical shift in the spectrum 
C)  should have neither the smallest nor the greatest chemical shift in the spectrum 
A)  should have the smallest chemical shift in the spectrum 
B)  should have the greatest chemical shift in the spectrum 
C)  should have neither the smallest nor the greatest chemical shift in the spectrum

Question 8

An unknown compound has a molecular formula of C5H8. Deduce the structure by using the proton and carbon NMR spectra provided.

Accepted Answer

First calculate the degree of unsaturati

Question 9

How many signals would you expect in a 13C NMR spectrum for this compound? Identify the carbon with the highest chemical shift.

Accepted Answer

Six signals are expected for the ¹³C NMR s

Question 10

A compound X with the formula C4H10O2 has the NMR spectrum shown. The integrals are given over their respective resonances, and the J values are coupling constants. Deduce the structure of compound X and explain how you came to this conclusion. Hints: (1) The only chemical shift information you need is that protons on carbons F1F1F1S1F1F1F10 to an oxygen have chemical shifts in the F1F1F1S1F1F1F10 3.2-F1F1F1S1F1F1F10 4.0 range. (2) You do not need to interpret the complex splittings at F1F1F1S1F1F1F10 3.22, F1F1F1S1F1F1F10 3.37, and F1F1F1S1F1F1F10 3.9 to deduce the structure, but you will need to interpret the splittings in the gray boxes.

Accepted Answer

First calculate the degree of unsaturati

Question 11

Of the protons that are labeled, which set experiences the greatest magnetic field in an NMR spectrometer?

Accepted Answer

A)  a 
B)  b 
C)  c 
D)  d 
E)  e 
A)  a 
B)  b 
C)  c 
D)  d 
E)  e

Question 12

Consider how the NMR spectrum of protons a in the compound changes on the addition of a trace of acid (assume that Jab ≠ Jac):

Accepted Answer

A)  no change 
B)  from a doublet of doublets to a simple doublet 
C)  from a triplet to a singlet 
D)  from a doublet of doublets to a triplet 
E)  none of these choices 
A)  no change 
B)  from a doublet of doublets to a simple doublet 
C)  from a triplet to a singlet 
D)  from a doublet of doublets to a triplet 
E)  none of these choices

Question 13

11. Consider the ether:
  
-How many resonances should there be in the NMR spectrum of the compound? (A split resonance counts as one resonance.)

Accepted Answer

There are three resonances. Th

Question 14

a. Identify compound X with the formula C5H10O that has the IR and NMR spectra shown.
b. Compound X is subjected to catalytic hydrogenation (H2, Pd/C) to give compound Y. Give the structure of compound Y and describe the most significant difference between the NMR spectra of X and Y.

Accepted Answer

a. First calculate the degree of unsatur

Question 15

Consider the labeled protons in the compound.
  The resonance of protons c would appear in the NMR spectrum as

Accepted Answer

A)  a singlet. 
B)  a doublet. 
C)  a triplet. 
D)  a quartet. 
E)  an octet (an eight-line splitting pattern).f. 
some other splitting pattern. 
A)  a singlet. 
B)  a doublet. 
C)  a triplet. 
D)  a quartet. 
E)  an octet (an eight-line splitting pattern).f. 
some other splitting pattern.

Question 16

Deduce the structure of an unknown compound with a molecular formula of C4H8O given the following 13C NMR - DEPT spectrum. The numbers in parentheses indicate the number of attached hydrogens.
Proton decoupled 13C NMR: F1F1F1S1F1F1F10 23.3 (3), 68.5 (1), 116.4 (2), 135.7 (1)

Accepted Answer

First calculate the degree of unsaturati

Question 17

The NMR spectrum of the missing compound is given below the reaction. Draw the structure of the missing starting material.

Accepted Answer

We know from the reaction conditions tha

Question 18

Which letter corresponds to the set of protons that experience the greatest magnetic field when a sample of the compound is placed in the probe of an NMR spectrometer?

Accepted Answer

A)  a 
B)  b 
C)  c 
A)  a 
B)  b 
C)  c

Question 19

Consider the bolded protons in 1-propanol.
$$\mathrm { H } _ { 3 } \mathrm { C } - \mathrm { CH } _ { 2 } - \mathrm { CH } _ { 2 } - \mathrm { OH }$$ Following a "D2O shake," the splitting of the 1-propanol protons shown in bold type should be observed as

Accepted Answer

A)  a singlet. 
B)  a doublet. 
C)  a triplet. 
D)  a quartet. 
E)  some other splitting. 
A)  a singlet. 
B)  a doublet. 
C)  a triplet. 
D)  a quartet. 
E)  some other splitting.

Question 20

Deduce the structure of a compound C6H14O that corresponds to the proton NMR spectrum. The integral numbers are relative numbers of hydrogens. Assign each peak. There are no absorptions in the 3200-3600 cm-1 region of the IR.

Accepted Answer

First calculate the degree of unsaturati

Exam 14: Nuclear Magnetic Resonance Spectroscopy

Which compound contains two three-proton singlets in its NMR spectrum?

Deduce the structure of the unknown compound C6H12O, whose IR and NMR spectra are shown. Explain how you arrived at your structure. C6H12O\mathrm { C } _ { 6 } \mathrm { H } _ { 12 } \mathrm { O }C6​H12​O ​

Deduce a structure that corresponds to the molecular formula and NMR spectra. Explain how you arrived at this structure. ​ Molecular formula: C5H12O. 1H NMR:  1.18 (3H, t, J = 8 Hz);  1.13 (6H, d, J = 6.8 Hz);  3.53 (2H, q, J = 8.0 Hz);  3.65 (1H, septet, J = 6.8 Hz).

In an NMR spectrometer operating at ν0 = 300 MHz, a resonance that has a chemical shift of 2.0 ppm (i.e.,  2) occurs at a frequency that is

What radiation frequency (in sec-1, or Hz) is required to bring a set of protons into resonance if they experience a magnetic field of 50,000 gauss? Show your work.

7. Consider the NMR spectrum of the compound: -The protons labeled ________________.

An unknown compound has a molecular formula of C5H8. Deduce the structure by using the proton and carbon NMR spectra provided.

How many signals would you expect in a 13C NMR spectrum for this compound? Identify the carbon with the highest chemical shift.

Of the protons that are labeled, which set experiences the greatest magnetic field in an NMR spectrometer?

Consider how the NMR spectrum of protons a in the compound changes on the addition of a trace of acid (assume that Jab ≠ Jac):

11. Consider the ether: -How many resonances should there be in the NMR spectrum of the compound? (A split resonance counts as one resonance.)

a. Identify compound X with the formula C5H10O that has the IR and NMR spectra shown. b. Compound X is subjected to catalytic hydrogenation (H2, Pd/C) to give compound Y. Give the structure of compound Y and describe the most significant difference between the NMR spectra of X and Y.

Consider the labeled protons in the compound. The resonance of protons c would appear in the NMR spectrum as

Deduce the structure of an unknown compound with a molecular formula of C4H8O given the following 13C NMR - DEPT spectrum. The numbers in parentheses indicate the number of attached hydrogens. Proton decoupled 13C NMR:  23.3 (3), 68.5 (1), 116.4 (2), 135.7 (1)

The NMR spectrum of the missing compound is given below the reaction. Draw the structure of the missing starting material.

Which letter corresponds to the set of protons that experience the greatest magnetic field when a sample of the compound is placed in the probe of an NMR spectrometer?

Deduce the structure of a compound C6H14O that corresponds to the proton NMR spectrum. The integral numbers are relative numbers of hydrogens. Assign each peak. There are no absorptions in the 3200-3600 cm-1 region of the IR.

Chemical Bonding and Chemical Structure

Alkanes and Organic Nomenclature

The Curved-Arrow Notation, Resonance, Acids and Bases, and Chemical Equilibrium

Introduction to Alkenes and Alkynes

Addition Reactions of Alkenes and Alkynes

Principles of Stereochemistry

Cyclic Compounds and Reaction Stereochemistry

Nomenclature and Noncovalent Intermolecular Interactions

The Chemistry of Alkyl Halides

Free-Radical Reactions, Main-Group Organometallic Compounds, and Carbenes

The Chemistry of Alcohols and Thiols

The Chemistry of Ethers, Epoxides, Glycols, and Sulfides

Introduction to Spectroscopy

Dienes and Aromaticity

The Chemistry of Benzene and Its Derivatives

Allylic and Benzylic Reactivity

The Chemistry of Aryl Halides, Vinylic Halides, and Phenols

The Chemistry of Aldehydes and Ketones

The Chemistry of Carboxylic Acids

The Chemistry of Carboxylic Acid Derivatives

The Chemistry of Enolate Ions, Enols, and Α,β-Unsaturated Carbonyl Compounds

The Chemistry of Amines

Carbohydrates

The Chemistry of Thioesters, Phosphate Esters, and Phosphate Anhydrides

The Chemistry of the Aromatic Heterocycles and Nucleic Acids

Amino Acids, Peptides, and Proteins

Pericyclic Reactions

Filters

Deduce a structure that corresponds to the molecular formula and NMR spectra. Explain how you arrived at this structure. Molecular formula: C₅H₁₂O. ¹H NMR:  1.18 (3H, t, J = 8 Hz);  1.13 (6H, d, J = 6.8 Hz);  3.53 (2H, q, J = 8.0 Hz);  3.65 (1H, septet, J = 6.8 Hz).

In an NMR spectrometer operating at ν₀ = 300 MHz, a resonance that has a chemical shift of 2.0 ppm (i.e.,  2) occurs at a frequency that is

What radiation frequency (in sec^-1, or Hz) is required to bring a set of protons into resonance if they experience a magnetic field of 50,000 gauss? Show your work.

An unknown compound has a molecular formula of C₅H₈. Deduce the structure by using the proton and carbon NMR spectra provided.

How many signals would you expect in a ¹³C NMR spectrum for this compound? Identify the carbon with the highest chemical shift.

Consider how the NMR spectrum of protons a in the compound changes on the addition of a trace of acid (assume that J_ab ≠ J_ac):

a. Identify compound X with the formula C₅H₁₀O that has the IR and NMR spectra shown. b. Compound X is subjected to catalytic hydrogenation (H₂, Pd/C) to give compound Y. Give the structure of compound Y and describe the most significant difference between the NMR spectra of X and Y.

Deduce the structure of an unknown compound with a molecular formula of C₄H₈O given the following ¹³C NMR - DEPT spectrum. The numbers in parentheses indicate the number of attached hydrogens. Proton decoupled ¹³C NMR:  23.3 (3), 68.5 (1), 116.4 (2), 135.7 (1)

Deduce the structure of a compound C₆H₁₄O that corresponds to the proton NMR spectrum. The integral numbers are relative numbers of hydrogens. Assign each peak. There are no absorptions in the 3200-3600 cm^-1 region of the IR.