Spectroscopy ranges

Question 1

NMR Spetroscopy

Answer 1

Obtain information on chemical & structural environment of nuclei

Question 2

IR Spectroscopy

Answer 2

Information about types of bonds present

Question 3

Mass Spectrometry

Answer 3

Technique effectively weighs molecules

Question 4

UV/Vis Spectroscopy

Answer 4

Gives a characteristic absorption spectrum

Question 5

X-Ray Crystallography

Answer 5

Determines the position of atoms within a crystal

Question 6

Elemental analysis

Answer 6

Percentage-by-mass of elements in a compound determined

Question 7

HNMR 0-3ppm

Answer 7

Protons bonded to sp3 C without electronegative

Question 8

HNMR 3-5ppm

Answer 8

Protons bonded to sp3 C with electronegative

Question 9

HNMR 5-10ppm

Answer 9

Protons bonded to sp2 C (double bonds & aromatic)

Question 10

HNMR Coupling and Integration

Answer 10

Coupling present (usually seen over 3 bonds), Integration possible as area proportional to protons responsible

Question 11

HNMR Solvents

Answer 11

Deuterochloroform (CDCl3) = 7.26ppm

Deuteromethanol (CD3OD) = 3.35ppm (quintet), 4.8ppm

d6-Dimethyl sulphoxide (d6-DMSO, (CD3)2SO) = 2.50ppm (quintet)

Question 12

HNMR Amine RNH2 or R2NH

Answer 12

0.5 -4.5ppm

Question 13

HNMR Aromatic amines ArNH2 or ArNHR

Answer 13

3-6ppm

Question 14

HNMR Amides RCONH2 or RCONHR

Answer 14

5-12ppm

Question 15

HNMR Alcohols ROH

Answer 15

0.5 - 4.5ppm

Question 16

HNMR Phenols ArOH

Answer 16

4.5 - 10ppm

Question 17

HNMR Carboxylic acids RCOOH

Answer 17

9-15ppm

Question 18

HNMR How to improve OH & NH peaks

Answer 18

Peaks very broad and coupling not usually seen due to proton exchange
If rate slowed down, OH & NH signals become sharper & couplings seen -> achieved using d6-DMSO as solvent or making very dilute sample

Question 19

13CNMR 0-50ppm

Answer 19

sp3 C without electronegative

Question 20

13CNMR 50-100ppm

Answer 20

sp3 C with electronegative

Question 21

13CNMR 100-150ppm

Answer 21

sp2 C (double bonds & aromatic) without electronegative

Question 22

13CNMR 150-200ppm

Answer 22

sp2 C with electronegative

Question 23

13CNMR Carbonyl Acids/Amides

Answer 23

160-175ppm

Question 24

13CNMR Aldehyde & Ketones

Answer 24

~200ppm, Ketones typically just over, Aldehydes typically just under

Question 25

13CNMR C=N

Answer 25

Usually in 150-200ppm range but can be as low as 120ppm

Question 26

13CNMR Electronegative substituents

Answer 26

Oxygen = +50ppm Chlorine = +30ppm Alkyl = +9ppm Phenyl ring/C=C = +20ppm

Question 27

13CNMR Coupling and Integration

Answer 27

Coupling usually not taken into account as 13C spectra proton decoupled & Integration can't be used as size of peak may be qualitative indicator but not always the case e.g. quaternary C resonances usually weaker as no protons attached to make it relax faster

Question 28

13CNMR Solvents

Answer 28

Deuterochloroform (CDCl3) = 77.0 ppm (1:1:1 triplet) Deuteromethanol (CD3OD) = 49.1 ppm (septet) d6-Dimethyl sulphoxide (d6-DMSO, (CD3)2SO) = 39.6ppm (septet)

Question 29

IR four regions

Answer 29

2500 - 4000cm^-1 = Vibrations of X-H 2000 - 2500cm^-1 = Vibrations of Triple bonds 1500 - 1900cm^-1 = Vibrations of Double bonds <1500cm^-1 = Fingerprint region

Question 30

IR C-H

Answer 30

2900-3200cm^-1 (sharp but usually multiple so peak spread out)

Question 31

IR O-H

Answer 31

3500-3600cm^-1 (sharp, if not involved in H bonding) | 2900-3500cm^-1 (broad, if involved in H bonding)

Question 32

IR N-H

Answer 32

~3300cm^-1 (sharp)

Question 33

IR NH2

Answer 33

~3300cm^-1 (sym) & ~3400cm^-1 (asym) [sharp,strong]

Question 34

IR R-CN

Answer 34

2220 -2260cm^-1

Question 35

IR R-CC-H

Answer 35

2100-2140cm^-1

Question 36

IR R-CC-R'

Answer 36

~2200cm^-1 (weak)

Question 37

IR RCOCl (acid chloride)

Answer 37

1750-1815cm^-1 (sharp & strong)

Question 38

IR RC(O)OC(O)R (acid anhydride)

Answer 38

1740-1790cm^-1 (asym) & 1800-1850cm^-1 (sym) [sharp & strong]

Question 39

IR ROC(O)OR (carbonates)

Answer 39

1740-1780cm^-1 (sharp & strong)

Question 40

IR RCOOR (ester)

Answer 40

1735-1750cm^-1 (sharp & strong)

Question 41

IR RC(O)H (aldehyde)

Answer 41

1730cm^-1 (sharp & strong)

Question 42

IR R2C=O (ketone)

Answer 42

1715cm^-1 (sharp & strong)

Question 43

IR RCOOH (carboxylic acid)

Answer 43

1700-1740cm^-1 (sharp & strong)

Question 44

IR RCONR2 (amide)

Answer 44

1640-1690cm^-1 (sharp & strong)

Question 45

IR RCO2- (carboxylate anion)

Answer 45

1300-1420cm^-1 & 1550-1610cm^-1 (sharp & strong)

Question 46

IR C=C

Answer 46

~1640cm^-1 (weak)

Question 47

IR Benzene rings

Answer 47

1500-1600cm^-1 (2 or 3 sharp absorptions)

Question 48

IR NO2 (nitro groups)

Answer 48

1350cm^-1 (sym) and 1530cm^-1 (asym)

Question 49

IR Fingerprint region

Answer 49

many kind of bond vibrations found here, highly specific for each individual compound. Peaks not usually selected from here to individually assign

Question 50

Mass Spectra ionisation technique

Answer 50

electrospray = (M+H)+ | electron impact = M+

Question 51

CNMR Alkyne (sp C)

Answer 51

70-100ppm

Question 52

IR Vibrating Diatomic formula

Answer 52

f = ((2[pi]c)^-1)(k/μ)^0.5 where μ = m1m2/(m1+m2)

Question 53

IR Absorption criterion

Answer 53

If no change in the dipole moment when the bond stretches then it will not absorb IR at all

Question 54

IR Carbonyl strengthening/weakening

Answer 54

Anything that strengthens C=O give rise to absorption at higher freq ->strengthened by electron withdrawing Anything that weakens C=O give rise to absorption at lower freq -> weakened by electron donating

Question 55

IR Conjugation

Answer 55

Lowers base frequency by 20-30cm^-1

Question 56

IR ring structure

Answer 56

smaller the ring size, higher the stretching frequency -> doesn't alter strength of bond significantly but increases resistance via repulsion