Chapter 9 - NMR

Question 1

In proton NMR, the total number of signals describes how many __ types of __ there are.

Answer 1

different; hydorgens

Question 2

This term describes how shielded or de-shielded hydrogens are.

Answer 2

chemical shift

Question 3

What does the height of proton NMR signals signify? Give the term and definition.

Answer 3

Signal height is called integration; it describes the relative ratios of each type of hydrogen (**NOT the absolute number!)

Question 4

Multiplicity of proton NMR peaks is also known as __-__. What does it describe?

Answer 4

spin-spliting. It describes the number of neighboring H with a different signal (adjacent H will NOT split if they are symmetrical).

Question 5

T or F: In order for protons to be diastereotopic, there must be a chiral center 3J away from the protons.

Answer 5

False - a chiral center can be anywhere on the molecule.

Question 6

Proton NMR Ranges - list the ranges for the following:

a) 1°C (methyl) to 3°C
b) Allylic to a double bond, an aromatic ring, or a carbonyl group (all non-methyl); or at a terminal alkyne (vinyllic)
c) Allylic to an EN (Z-C-H)
d) Terminal double bond (vinyllic)
e) Hydroxyl or amino groups
f) ArOH
g) ArH
h) aldehyde
i) carboxylic acid

Answer 6

a) 0.8 - 1.8
b) ~2 - 3
c) ~3 - 4
d) ~4.5 - 6
e) ~1 - 6
f) ~4.5 - 7.5
g) ~6 - 8.5
h) ~9.5 - 10.5
i) ~10 - 13

Question 7

Why are splits of aromatic rings ugly?

Answer 7

They don’t follow the n + 1 rule; their J values are different not 6 Hz, and if there are substituents, forget about it!

Question 8

Common spin-splitting patterns in HNMR:

a triplet and a quartet.

Answer 8

an ethyl group (R-CH2-CH3)

Question 9

Common spin-splitting patterns in HNMR:

Two triplets

Answer 9

an ethylene group (R-CH2-CH2-R)

Question 10

Common spin-splitting patterns in HNMR:

a doublet and a septet

Answer 10

Isopropyl

Question 11

Common spin-splitting patterns in HNMR: singlets

Answer 11

quaternary groups (R3-C-CH3)

Question 12

CNMR ranges:

a) double bond
b) triple bond
c) EN
d) benzene
e) carbonyl

Answer 12

a) 100 - 140
b) 65 - 100
c) 30 - 80
d) 120 - 150
e) 160 - 210

Question 13

IR spectroscopy ranges (include broad/sharp or strength):

a) ArOH
b) Carboxylic acid
c) Carbonyl group (aldehydes, ketones, esters, carboxylic acid, and amides)
d) Amines
e) Nitrile (C≡N)
f) aldehydes (CHO)
g) ether (C-O)

Answer 13

a) ~3600 and sharp but variable strength in dilute solutions; 3200 - 3500 and strong and broad in H bonded(???)
b) 2500 - 3000; broad and variable in strength
c) 1690 - 1780; strong and in the order listed in the question (from lowest to highest)
d) 3300 - 3500; medium strength
e) ~2200 - 2300 range; medium strength
f) ~2700; medium to weak and sharp.
g) Fingerprint region

Question 14

In CNMR, DEPT-90 reveals only __ groups. DEPT-135 detects __, __, and __ groups; additionally, negative peaks signify __ groups, positive peaks signify __ or __ groups.
Neither DEPT-90 nor DEPT-135 detect __ carbons.

Answer 14

CH

CH, CH2, and CH3;
CH2;
CH, CH3

single