Ch 13 NMR spectra

Question 1

δ ¹HNMR

Answer 1

δ 0.9

Question 2

δ ¹HNMR

Answer 2

δ 1.3

Question 3

δ ¹HNMR

Answer 3

δ 1.4

Question 4

δ ¹HNMR

Answer 4

δ 2.1

Question 5

δ ¹HNMR

Answer 5

δ 2.5

Question 6

δ ¹HNMR

Answer 6

δ 3-4

Question 7

δ ¹HNMR

Answer 7

δ 5-6

Question 8

δ ¹HNMR

Answer 8

δ 1.7

Question 9

δ ¹HNMR

Answer 9

δ 7.2

Question 10

δ ¹HNMR

Answer 10

δ 2.3

Question 11

δ ¹HNMR

Answer 11

δ 9-10

Question 12

δ ¹HNMR

Answer 12

δ 10-12

Question 13

δ ¹HNMR

Answer 13

δ 2-5 (variable)

Question 14

δ ¹HNMR

Answer 14

δ 4-7 (variable)

Question 15

δ ¹HNMR

Answer 15

δ 1.5-4 (variable)

Question 16

δ ¹HNMR

Answer 16

δ 4.3 (F: χ = 4.0)

Question 17

δ ¹HNMR

Answer 17

δ 3.4 (OH: χ = 3.4)

Question 18

δ ¹HNMR

Answer 18

δ 3.0 (Cl: χ = 3.2)

Question 19

δ ¹HNMR

Answer 19

δ 2.7 (Br: χ = 3.0)

Question 20

δ ¹HNMR

Answer 20

δ 2.2 (I: χ = 2.7)

Question 21

what happens to deshielding shifts (δ) when more than one electron-withdrawing group is present?

Answer 21

If more than one electron-withdrawing group is present, the deshielding effects are nearly (but not quite) additive. In the chloromethanes the addition of the first chlorine atom causes a shift to δ 3.0, the second chlorine shifts the absorp- tion further to δ 5.3, and the third chlorine moves the chemical shift to δ 7.2 for chloroform. The chemical shift difference is about 2 to 3 ppm each time another chlorine atom is added, but each additional chlorine moves the peak slightly less than the previous one did.

Question 22

chemical shift (ppm) =

Answer 22

Question 23

what signal is δ 0 (0 ppm) on a ¹HNMR?

Answer 23

tetramethylsilane (TMS), ((CH₃)₄Si), the substance used as the reference point in ¹HNMR. Because silicon is less electronegative than carbon, the methyl groups of TMS are relatively electron-rich, and their protons are well shielded. They absorb at a higher field strength than most hydrogens bonded to carbon or other elements, so most NMR signals appear downfield (to the left, deshielded) of the TMS signal. All 12 protons in TMS absorb at exactly the same applied magnetic field, giving one strong absorption.