Structural analysis

Question 1

IR stretch c=o

Answer 1

1780-1650

Question 2

IR stretch c=n

Answer 2

2260-2220

Question 3

benzene / phenyl

Answer 3

1600 and 1500-1430

Question 4

1600 and 1500-1430

Answer 4

benzene / phenyl

Question 5

2260-2220

Answer 5

IR stretch c=n

Question 6

1780-1650

Answer 6

IR stretch c=o

Question 7

o-h alcohol

Answer 7

3650-3200

Question 8

o-h carboxylic acid

Answer 8

3300- 2500

Question 9

3300- 2500

Answer 9

o-h carboxylic acid

Question 10

3650-3200

Answer 10

o-h alcohol

Question 11

if a mass spec has two lines for m+ it means …

Answer 11

it has a atom with an isotope (maybe br or cl is present)

Question 12

mass spec : 29 means ….

Answer 12

ch2-ch3 chain (ethyl group)

Question 13

mass spec : 127 means ….

Answer 13

iodine

Question 14

mass spec: to signify iodine we may see…

Answer 14

127 and a large gap to the next group

Question 15

if br or cl is present , the m+ line is likely to look like what?

Answer 15

two lines for m+ because they can have an isotope

Question 16

mass spec : 77 means ….

Answer 16

phenyl group

Question 17

m*+1 = x . how do we work out how many carbons?

Answer 17

x/1.1

Question 18

HNMR: how can we work out if its a ch, ch2 or ch3 easily?

Answer 18

use the integration. if we know what one integral represents, we can compare this value to work out how many Hs are present in the others.

Question 19

mass spec : 91 means ….

Answer 19

tropylium aka benzene with a ch2

Question 20

HNMR: when two protons are coupled, the coupling constant is …

Answer 20

the same for both protons.
(therefore we can tell which peaks on hnmr are potentially coupled).

Question 21

HNMR: if the signals are zoomed in but look different, this is because…

Answer 21

they may be taken at different frequencies. look carefully to see if they have been taken under different equipment.

Question 22

HMRS (High resolution mass spectrometry)

Answer 22

sum of the exact values of the masses of the most common isotope eg c-12.00000 h+1.007825

Question 23

HNMR: isopropyl group looks like …

Answer 23

septuplet

Question 24

very small coupling constants mean that its a…

Answer 24

long range coupling

Question 25

ennantiomers are ….

Answer 25

if you swith the protons for x, they are mirror images or each other.

Question 26

diastereomers are…

Answer 26

if you swith protons for x, they are totally different molecules. can occur when switching for x creates two or more chiral centres (doesnt always occur)

Question 27

ir- alcohol

Answer 27

broad round band at 3200-3400

Question 28

ir- alkene ch

Answer 28

sharp stalegtite shape band at above 3000

Question 29

ir - alkane ch

Answer 29

sharp stalegtite shape band at below 3000

Question 30

ir carbonyls c=o

Answer 30

strong very sharp pointy stretch at 1700

Question 31

ir alkene c=c

Answer 31

a few sharp bands at around 1600

Question 32

ir single c-o bond

Answer 32

medium thickness v shaped band at 1100

Question 33

ir alkyne ch

Answer 33

sharp medium intensity at 3300

Question 34

ir NH

Answer 34

either a very intense sharp band (maybe more for nh) or a slighly broader, less intense w shape . both at 3500.

Question 35

hnmr sections as we increase from 0

Answer 35

(not ppm just numbered for ease)
1- alkane and alkane like hydrogens
2- hydrogens adjacent to an unstaurated bond eg ketones or allylic hydrogens
3- SP hydrogens on a triple bond
4- hydrogens adjacent to electronegative atoms
5- Alkene SP2 hydrogens
6- Aromatic hydrogens
7- Aldehydes

Question 36

Calculating J values for first order splitting eg s d t q q s etc

Answer 36

will only have one J value.
(ppm1(highest but also doesnt matter really as long as they are next to eachother)-ppm2) x frequency of NMR machine

Question 37

Calculating J values for second order splitting eg dd dt dq etc

Answer 37

will have 2 J values.
J1= (ppmbigpart1-ppmsamebigpartin2) x freq NMR machine
J2= ppm1-ppm2 (like you do for first order splitting)

J1 = J value of overall doublet
J2= J value of mini doublets

Question 38

coupling constanats are highest for dihedral angles of …. and lowest for dihedral angles of….

Answer 38

highest 180. lowest 0