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Organic Chemistry > Spectroscopy > Flashcards

Spectroscopy Flashcards

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1
Q

electromagnetic radiation

A

exhibits wave-like behaviour

consists of oscillating electric and magnetic fields

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2
Q

photon

A

packets of EM radiation

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3
Q

wavenumber

A

reciprocal of wavelength

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4
Q

1 DBE

A

1 ring or 1 double bond

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5
Q

2 DBE

A

2 rings or 2 double bonds or 1 ring + double bond

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6
Q

4 DBE

A

benzene ring ( 3 for each double bond + 1 for ring)

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7
Q

total energy of molecule is a combination of what?

A

electronic, vibrationional and rotational energies

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8
Q

how does electronic (UV/Vis) spec work?

A

wavelength of light absorbed = energy required to move an electron from lower -> higher energy level

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9
Q

chromophore

A

part of molecule that absorbs UV-vis photon

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10
Q

bathochromic shift

A

change to longer wavelength

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11
Q

hypsochromic shift

A

change to shorter wavelength

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12
Q

hyperchromicity

A

increase in absorbance

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13
Q

hypochromicity

A

decrease in absorbance

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14
Q

Beer-Lambert Law

A

links concentration to absorbance via molar extinction coefficient

once we know molar-extinction coefficient, we can work out conc. of unknown sample

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15
Q

Hooke’s law

A

describes movement of 2 masses attached to spring

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16
Q

I values

A

odd masses = 1/2 spin

odd numbers of protons and odd numbers of neutrons = integral spin

even numbers of protons/neutrons = zero spin

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17
Q

relationship with electrons and frequency in NMR spectra

A

electron donating = more shielding = lower frequency

electron withdrawing = less shielding = higher frequency

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18
Q

APT

A

[attached proton test]

CH and CH3 = up

CH2 and CH4 = down

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19
Q

1H NMR

A

use integral to work out number of protons in each environment (ratio)

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20
Q

coupling

A

interaction between nuclei and nearby hydrogen nuclei to give multiple peaks

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21
Q

precession

A

slow movement of axis of a spinning body

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22
Q

unit of chemical shift

A

ppm

allows it to be independent of spec. frequency

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23
Q

resolution

A

ability to distinguish between 2 points

24
Q

what happens to the resolution as you increase the spec. frequency?

A

[increase in spec. frequency = increase in strength of magnet]

increases resolution

25
Q

advantage of using stronger magnet

A

higher resolution

greater sensitivity (can use less sample)

26
Q

diamagnetism

A

when e- placed in magnetic field, they will circulate -> generates electric current -> induces magnetic field

induced magnetic field opposes applied magnetic field (opposing directions)

27
Q

intramolecular factors that affect chemical shift

A

inductive effects

anisotropy

resonance

Van der Waals forces

isotope effects

28
Q

intermolecular factors that affect chemical shift

A

temperature

hydrogen bonds

solvent

29
Q

inductive effects

A

EWG remove e- density = deshielding = higher frequency

30
Q

isotropic effect

A

sub. with heavier isotope, NMR = lower frequency

exerts influence on all spatial directions

31
Q

anisotropic effect

A

exerts influence non-uniformly (has direction)

i.e. local magnetic fields induced by e- in particular parts of molecule

32
Q

chemical shift equivalent

A

when 2 protons are interchangeable by rapid process or symmetry operation

33
Q

symmetry operation

A

movement of an object so that new object is is indistinguishable from original

34
Q

homotopic

A

protons have identical chemical shift

35
Q

diastereotopic

A

protons are chemical shift INequivalent

any pair of protons next to chiral centre = diastereotopic

36
Q

what happens when the interchange of protons is rapid?

A

average of chemical shifts is taken

37
Q

resolving peaks

A

peaks are resolved as long as the rate of rotation is </= to rate of introversion

38
Q

why does coupling arise?

A

interaction of nuclear spins with electronic spins in the bond

39
Q

what can isolate a spin system?

A

heteroatom or quaternary carbon

40
Q

geminal

A

same carbon

41
Q

vicinal

A

on adjacent carbons

42
Q

long range

A

more than 4 bonds apart

43
Q

does strong coupling result in a small or large J value?

A

large J value

44
Q

what does the magnitude of J depend on?

A

geometry - e.g. cis/trans

no. of bonds - increase no. of bonds = decrease strength of coupling

heteroatoms

angle strain

bond strength

hybridisation

45
Q

first order splitting pattern

A

follows Pascal’s triangle

46
Q

STICK DIAGRAMS - when are the intensities all the same?

A

when I > 1/2

47
Q

second order

A

[occurs when δ is similar - ROOFING is observed]

diastereotopic protons

alkene systems with similar sub.

para sub. benzene

48
Q

when are 2 nuclei magnetically equivalent?

A

chemical shift is equivalent + coupled equally to other nuclei in spin system

49
Q

magnetic equivalence

A

2 nuclei have identical coupling with the same identical partner(s)

50
Q

coupling to protons on heteroatoms - OXYGEN

A

doesn’t generally occur

due to rapid proton exchange with H2O or impurities

51
Q

coupling to protons on heteroatoms - NITROGEN/AMINES

A

N has quadrupole moment (non-spherical charge distribution)

proton exchange = rapid (like OH)

52
Q

D2O shake

A

identifies OH, NH2 and amide protons

add + then rerun spectrum (peak disappears)

53
Q

satellites

A

coupling of protons to 13C (1.1% abundant) rather than other protons

54
Q

coupling to protons on heteroatoms - FLUORINE

A

19F = 1/2 I

100% abundant

large J values + long range

55
Q

2D NMR - COSY

A

coupling through bonds

56
Q

2D NMR NOESY

A

space

Organic Chemistry (13 decks)

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