Free Practice Quiz Question List

02 Spectroscopic Structure Elucidation Online Quiz Questions

Use this free practice quiz with 20 questions to review 02 Spectroscopic Structure Elucidation, test your knowledge, and prepare for your next test or exam.

20 questions

True or false

1 point

In an electron-ionization mass spectrum, the base peak is necessarily the molecular ion. True or false?

A
True
B
False

True or false

1 point

The position of a strong carbonyl absorption by itself always identifies the specific type of carbonyl compound. True or false?

A
True
B
False

Fill in the blank

1 point

The IR region around $1500\text{–}500\ \mathrm{cm}^{-1}$ , with many overlapping bands useful for sample comparison, is called the .

Choose one

1 point

What is the degree of unsaturation (DBE) of $\mathrm{C_5H_8O_2}$ ?

True or false

1 point

In a broadband-decoupled $^{13}\mathrm{C}$ NMR spectrum, molecular symmetry can make the number of signals smaller than the number of carbon atoms. True or false?

A
True
B
False

Written response

1 point

A soft-ionization spectrum shows an $[M+H]^+$ ion at $m/z=153$ . What is the neutral molecule’s nominal mass?

Choose one

1 point

An IR spectrum has a distinct, medium-to-strong band near $2240\ \mathrm{cm}^{-1}$ . Which group is most strongly indicated by this clue?

A
Nitrile
B
Alcohol
C
Carbonyl
D
Alkane

Written response

1 point

Calculate the DBE of $\mathrm{C_6H_{10}O}$ . Enter the result as a number.

Choose all

1 point

Select all statements supported by the principles of proton NMR interpretation.

A
Integration estimates the relative number of hydrogens represented by a signal.
B
In simple cases, coupling to $n$ neighboring hydrogens gives $n+1$ lines.
C
Every O–H and N–H proton follows the $n+1$ rule without exception.
D
A chemical shift alone gives the exact number of hydrogens in a signal.
E
Overlapping signals can complicate the interpretation of splitting.

Fill in the blank

1 point

A small $M+1$ peak is commonly due mainly to naturally occurring .

Choose one

1 point

How many DBE does one triple bond contribute?

Choose all

1 point

Select all correct statements about isotope patterns that can help constrain a molecular formula.

A
Chlorine often gives an $M$ and $M+2$ pair in an approximate $3:1$ ratio.
B
Bromine often gives an $M$ and $M+2$ pair in an approximate $1:1$ ratio.
C
Chlorine and bromine both typically give an approximate $1:1$ ratio.
D
An approximate $3:1$ ratio is characteristic of bromine rather than chlorine.
E
Isotope patterns can support an inference about a molecule’s halogen content.

Open ended

1 point

An unknown has formula $\mathrm{C_4H_8O_2}$ and an EI molecular-ion peak at $m/z=88$ . Its IR spectrum has a strong carbonyl absorption and strong C–O-region bands, with no broad alcohol or acid O–H absorption. Its $^{1}\mathrm{H}$ NMR has a quartet integrating to $2\mathrm{H}$ near $4.1\ \mathrm{ppm}$ , a singlet integrating to $3\mathrm{H}$ near $2.0\ \mathrm{ppm}$ , and a triplet integrating to $3\mathrm{H}$ near $1.3\ \mathrm{ppm}$ . Its $^{13}\mathrm{C}$ NMR has four distinct environments. Explain how these observations collectively support a proposed structure, and why no single observation proves the identity on its own.

Choose one

1 point

An IR spectrum has a distinct medium-to-strong absorption near $2230\ \mathrm{cm^{-1}}$ . Which functional group is most strongly indicated?

A
An alkane C–H stretch
B
A nitrile C≡N stretch
C
An alcohol O–H stretch
D
An aromatic C=C stretch

Choose one

1 point

A lower-resolution mass spectrum shows molecular-ion peaks at $m/z$ 150 and 152 with approximately equal intensity. Which element is most strongly suggested?

A
A chlorine atom
B
A large number of carbon atoms
C
A bromine atom
D
A molecular ion that has lost a proton

Choose one

1 point

A broadband-decoupled $^{13}\mathrm{C}$ NMR spectrum contains a signal near $190\ \mathrm{ppm}$ . Which interpretation best fits this chemical shift?

A
A signal near 190 ppm is consistent with a carbonyl carbon.
B
A signal near 190 ppm is typical of a saturated alkyl carbon.
C
A signal near 190 ppm is typical of a carbon bonded to oxygen but not part of a carbonyl.
D
A signal near 190 ppm rules out a carbonyl group.

Written response

1 point

Calculate the degree of unsaturation for a compound with formula $\mathrm{C_5H_8O}$ , using $\mathrm{DBE} = \frac{2C+2+N-H-X}{2}$ .

Choose one

1 point

A proton is moved from a simple alkyl environment to an environment near an electronegative atom. What general chemical-shift change should you expect?

A
They generally move signals upfield to lower ppm.
B
They eliminate the possibility of equivalent nuclei.
C
They affect only integration, not chemical shift.
D
They generally move signals downfield to higher ppm.

Choose one

1 point

A singly charged $[M+H]^+$ ion appears at nominal $m/z$ 89. What is the neutral molecule's nominal mass?

A
89
B
88
C
90
D
It cannot be estimated without knowing the base peak.

Written response

1 point

A molecule has more carbon atoms than distinct signals in its broadband-decoupled $^{13}\mathrm{C}$ NMR spectrum. What structural property can account for multiple carbons giving the same signal?