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Return to NMR Spectroscopy in Inorganic Chemistry 2e Student resources
Chapter 3 Multiple Choice Questions
Factors influencing the chemical shift and coupling constants
*
not completed
.
The diamagnetic contribution to shielding is
dominant for light atoms and is generally insensitive to changes in the chemical environment, resulting in a narrow range of chemical shifts for light atoms.
correct
incorrect
dominant for heavy atoms and is generally insensitive to changes in the chemical environment, resulting in a narrow range of chemical shifts for heavy atoms.
correct
incorrect
dominant for heavy atoms and is generally sensitive to changes in the chemical environment, resulting in a narrow range of chemical shifts for heavy atoms.
correct
incorrect
dominant for light atoms and is generally sensitive to changes in the chemical environment, resulting in a broad range of chemical shifts for light atoms.
correct
incorrect
*
not completed
.
The paramagnetic contribution to shielding is
dominant for light atoms and provides important information about the electronic structure and bonding in molecules and results in a significantly broader range of chemical shifts.
correct
incorrect
dominant for heavy atoms and provides important information about the electronic structure and bonding in molecules and results in a significantly narrower range of chemical shifts.
correct
incorrect
dominant for heavy atoms and provides important information about the electronic structure and bonding in molecules and typically results in a significantly broader range of chemical shifts.
correct
incorrect
dominant for light atoms and provides important information about the electronic structure and bonding in molecules and typically results in a significantly narrower range of chemical shifts.
correct
incorrect
*
not completed
.
The symmetry in complexes is an important factor affecting chemical shifts. For
fac
-Mo(CO)
3
(PPh
3
)
3
, how many signals due to CO will appear in
13
C{
1
H} NMR spectrum?
Two signals due to CO as only two carbonyls from three are equivalent.
correct
incorrect
Three signals due to CO as all the carbonyls are equivalent by being placed trans to PPh
3
.
correct
incorrect
Three signals due to CO as all the carbonyls are non-equivalent.
correct
incorrect
One signal due to CO as all the carbonyls are symmetry equivalent by being placed
trans
to PPh
3
.
correct
incorrect
*
not completed
.
The oxidation state of the element is known to affect its chemical shift. For P(III) versus P(V)
chemical shifts of
31
P for P(III) compounds are only known as P(V) is paramagnetic.
correct
incorrect
chemical shifts of
31
P for P(III) compounds are deshielded when compared to P(V).
correct
incorrect
chemical shifts of
31
P for P(III) compounds are nearly identical to those of P(V).
correct
incorrect
chemical shifts of
31
P for P(III) compounds are shielded when compared to P(V).
correct
incorrect
*
not completed
.
For the silicon(IV) tetrahalides, replacement of the halogen in the order Cl to Br to I, will result in
an increase in deshielding and consequently lower/less positive chemical shifts for
29
Si on going from Cl to Br to I.
correct
incorrect
an increase in shielding and consequently lower/less positive chemical shifts for
29
Si on going from Cl to Br to I.
correct
incorrect
an increase in deshielding and consequently higher/more positive chemical shifts for
29
Si on going from Cl to Br to I.
correct
incorrect
an increase in shielding and consequently higher/more positive chemical shifts for
29
Si on going from Cl to Br to I.
correct
incorrect
*
not completed
.
Adding small amounts of Cr(III) compounds to the sample during acquisition of
13
C{
1
H} spectra
may result in significantly slower relaxation of
13
C spins, particularly affecting quaternary carbon centres due to the contribution of the paramagnetic relaxation pathway.
correct
incorrect
may result in significantly faster relaxation of
13
C spins due to the contribution of the quadrupolar relaxation pathway, particularly affecting protonated carbon centres.
correct
incorrect
may result in significantly faster relaxation of
13
C spins due to the contribution of the paramagnetic relaxation pathway particularly affecting the detection of quaternary carbon centres.
correct
incorrect
has no effect on
13
C{
1
H} acquisition.
correct
incorrect
*
not completed
.
Chiral lanthanide shift reagents can be used to
separate the signals of individual enantiomers of target compounds in solution through the formation of diastereomers exhibiting different chemical shifts.
correct
incorrect
separate the signals of isomers of target compounds in solution through the formation of enantiomers exhibiting different chemical shifts.
correct
incorrect
separate the signals of rotamers of target compounds in solution through the formation of enantiomers exhibiting different chemical shifts.
correct
incorrect
separate the signals of individual enantiomers of target compounds in solution through the formation of diastereomers exhibiting similar chemical shifts.
correct
incorrect
*
not completed
.
A reduced coupling constant is introduced to
remove the influence of the natural abundance of spins when comparing the coupling constants for any selected pair of nuclei.
correct
incorrect
remove the influence of the gyromagnetic ratios when comparing the coupling constants for any selected pair of nuclei.
correct
incorrect
remove the influence of the coupling constant when estimating the gyromagnetic ratios of a pair of nuclei.
correct
incorrect
remove the influence of the gyromagnetic ratios when comparing the chemical shifts of pair of nuclei.
correct
incorrect
*
not completed
.
Consider
1
J
(PtP) in
cis
-[PtCl
2
(PBu
3
)
2
] and
cis
-[PtCl
2
(P(OBu)
3
)
2
]
the coupling constant will be larger in
cis
-[PtCl
2
(P(OBu)
3
)
2
] since the electronegativity of the substituents on the phosphine ligand has increased.
correct
incorrect
the coupling constant will be larger in
cis
-[PtCl
2
(PBu
3
)
2
] since the electronegativity of the substituents on the phosphine ligand has increased.
correct
incorrect
the coupling constant will be larger in
cis
-[PtCl
2
(PBu
3
)
2
] since the electronegativity of the substituents on the phosphine ligand has decreased.
correct
incorrect
the coupling constant will be larger in
cis
-[PtCl
2
(P(OBu)
3
)
2
] since the electronegativity of the substituents on the phosphine ligand has decreased.
correct
incorrect
*
not completed
.
The size of the coupling constant can be used to judge the mutual placement of ligands at metal centre and the interbond angle
the coupling constant between similar groups will be larger if the coupling nuclei are mutually
cis
, and smaller for groups that are mutually
trans
.
correct
incorrect
coupling between similar groups that are mutually
trans
is generally too small to be visible.
correct
incorrect
the coupling constant between similar groups will be larger if the coupling nuclei are mutually
trans
, and smaller for groups that are mutually
cis
.
correct
incorrect
coupling constants are generally similar for both
trans
and
cis
coupled ligands and are mostly dependent of the metal centre used.
correct
incorrect
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