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Chapter 14: Q30P (page 527)

Which of the highlighted carbon atoms in each molecule absorbs farther downfield?

a.

b.

c.

d.

Short Answer

Expert verified

a.

b.

c.

d.

Step by step solution

01

Upfield and Downfield in \({}^{{\bf{13}}}{\bf{C}}\) NMR

The carbon atoms that absorb downfield are the ones that shows signal to the left of the NMR spectrum (higher chemical shifts).

The carbon atoms that absorb upfield are the ones that shows signal to the farther right of the NMR spectrum (lower chemical shifts).

02

Downfield shift in \({}^{{\bf{13}}}{\bf{C}}\)NMR

  • The presence of electronegative elements shifts the absorptions downfield.
  • The \(s{p^2}\) hybridized carbon atoms show downfield absorptions.
  • All the electron deficient carbon atoms (for example the carbonyl carbon) shows downfield absorptions.
03

Carbon atoms showing downfield absorptions in the given compounds.

a.

The carbon atom adjacent to the oxygen atom is electron-deficient and hence it absorbs downfield.

b.

The carbon atom bonded to two bromine atoms is highly electron-deficient compared to the other and hence it absorbs farther downfield.

c.

The carbonyl carbon absorbs downfield.

d.

The double-bonded carbon (\(s{p^2}\)hybridized) absorbs farther downfield.

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Most popular questions from this chapter

Question: Identify the structures of isomers A and B (molecular formula C9H10O ).

Compound A: IR peak at 1742 cm-1 ; 1 H NMR data (ppm) at 2.15 (singlet, 3 H), 3.70 (singlet, 2 H), and 7.20 cm-1(broad singlet, 5 H). Compound B: IR peak at 1688 ; 1 H NMR data (ppm) at 1.22 (triplet, 3 H), 2.98 (quartet, 2 H), and 7.28–7.95 (multiplet, 5 H).

Question: How many 1H NMR signals does each natural product exhibit?

a.

b.

c.

d.

Question: Draw the structure of a compound of molecular formula C4H8O that has a signal in its 13C NMR spectrum at > 160 ppm. Then draw the structure of an isomer of molecular formula C4H80 that has all of its 13C NMR signals at < 160 ppm.

What splitting pattern is observed for each proton in the following compounds?

a.

b.

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.
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