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Chapter 14: Q.21558-14-30P. (page 558)

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 13C 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 13C NMR

• The presence of electronegative elements shifts the absorptions downfield.

• The sp2 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.

Carbon atom absorbing downfield in a.

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

b.

Carbon atom absorbing downfield in b.

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

c.

Carbon atom absorbing downfield in c.

The carbonyl carbon absorbs downfield.

d.

Carbon atom absorbing downfield in d.

The double-bonded carbon ( hybridized) absorbs farther downfield.

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Most popular questions from this chapter

Question: Draw the four constitutional isomers having molecular formula C4H9Brand indicate how many different kinds of carbon atoms each has.

Question: The \(^{\bf{1}}{\bf{H}}\) NMR spectrum of \({\bf{C}}{{\bf{H}}_{\bf{3}}}{\bf{OH}}\) recorded on a 500 MHz NMR spectrometer consists of two signals, one due to the \({\bf{C}}{{\bf{H}}_{\bf{3}}}\) protons at 1715 Hz and one due to the OH proton at 1830 Hz, both measured downfield from TMS. (a) Calculate the chemical shift of each absorption. (b) Do the \({\bf{C}}{{\bf{H}}_{\bf{3}}}\) protons absorb upfield or downfield from the OH proton?

Draw all constitutional isomers of molecular formula C3H6Cl2.

a. How many signals does each isomer exhibit in its 1HNMR spectrum?

b.How many lines does each isomer exhibit in its 13CNMR spectrum?

c. When only the number of signals in both 1Hand 13C NMR spectroscopy is considered, is it possible to distinguish all of these constitutional isomers?

Question: Cyclohex-2-enone has two protons on its carbon-carbon double bond (labeled Ha and Hb ) and two protons on the carbon adjacent to the double bond (labeled Hc ). (a) If Jab = 11 Hz and Jbc = 4 Hz, sketch the splitting pattern observed for each proton on the hybridized carbons. (b) Despite the fact that Ha is located adjacent to an electron-withdrawing C=O, its absorption occurs up-field from the signal due to Hb(6.0 vs. 7.0 ppm). Offer an explanation.

For each compound give the number of NMR signals, and then determine how many peaks are present for each NMR signal.

a.

b.

c.

d.
See all solutions

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