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Chapter 14: Q.21558-14-49P (page 563)

Question: Rank the highlighted carbon atoms in each compound in order of increasing chemical shift.

a.

b.

Short Answer

Expert verified

Answer

a. Ca< Cb < Cc

b. Cc < Cb< Ca

Step by step solution

01

Chemical shift

13C spectroscopy gives a downfield (higher value) chemical shift and an upfield chemical shiftaccording to the non-equivalent chemical environment present around the atom which is under observation.

02

Explanation

a.

Labeled carbon

Ccis adjacent to the carbonyl oxygen which is an electronegative atom. Therefore, Cc has higher value of chemical shift. Cb is also close to carbonyl oxygen followed by Ca.

Therefore, the order of chemical shift value is shown as:

a. Ca < Cb < Cc

b.

Labeled carbon

Cahas higher value of chemical shift due to presence of sp2 hybridized atoms. Ccis adjacent to Br which is an electronegative atom. Therefore, CC has higher value of chemical shift. Cb is also close to the double bond.

Therefore, the order of chemical shift value is shown as:

b. Cc < Cb < Ca

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Most popular questions from this chapter

Identify the carbon atoms that give rise to the signals in the \)^{{\bf{13}}}{\bf{C}}\) NMR spectrum of each compound.

a. \){\bf{C}}{{\bf{H}}_{\bf{3}}}{\bf{C}}{{\bf{H}}_{\bf{2}}}{\bf{C}}{{\bf{H}}_{\bf{2}}}{\bf{C}}{{\bf{H}}_{\bf{2}}}{\bf{OH}}\); \)^{{\bf{13}}}{\bf{C}}\) NMR: 14, 19, 35, and 62 ppm

b. \){\left( {{\bf{C}}{{\bf{H}}_{\bf{3}}}} \right)_{\bf{2}}}{\bf{CHCHO}}\); \)^{{\bf{13}}}{\bf{C}}\) NMR: 16, 41, and 205 ppm

c. \){\bf{C}}{{\bf{H}}_{\bf{2}}}{\bf{ = CHCH}}\left( {{\bf{OH}}} \right){\bf{C}}{{\bf{H}}_{\bf{3}}}\); \)^{{\bf{13}}}{\bf{C}}\) NMR: 23, 69, 113, and 143 ppm

How can you use \(^{\bf{1}}{\bf{H}}\) NMR spectroscopy to distinguish between \({\bf{C}}{{\bf{H}}_{\bf{2}}}{\bf{ = C}}\left( {{\bf{Br}}} \right){\bf{C}}{{\bf{O}}_{\bf{2}}}{\bf{C}}{{\bf{H}}_{\bf{3}}}\)and methyl (E)-3-bromopropenoate, \({\bf{BrCH = CHC}}{{\bf{O}}_{\bf{2}}}{\bf{C}}{{\bf{H}}_{\bf{3}}}\)?

Label the signals due to \({{\bf{H}}_{\bf{a}}}\), \({{\bf{H}}_{\bf{b}}}\), and \({{\bf{H}}_{\bf{c}}}\) in the 1 H NMR spectrum of acrylonitrile \(\left( {{\bf{C}}{{\bf{H}}_{\bf{2}}}{\bf{ = CHCN}}} \right)\). Draw a splitting diagram for the absorption due to the \({{\bf{H}}_{\bf{c}}}\) proton.

Compound A exhibits two signals in its 1H NMR spectrum at 2.64 and 3.69 ppm and the ratio of the absorbing signals is 2:3. Compound B exhibits two signals in its 1H NMR spectrum at 2.09 and 4.27 ppm and the ratio of the absorbing signals is 3:2. Which compound corresponds to dimethyl succinate and which compound corresponds to ethylene diacetate?

Into how many peaks will each proton shown in green be split?

a.

b.

c.

d.

e.

f.
See all solutions

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