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year 2 spec > nmr 3 > Flashcards

nmr 3 Flashcards

1
Q

why do we use H1 nmr aka proton nmrrr

A

bc its ubiquitous - its present in nearly all organic and inorganic metal complexes

spin 1/2 nuc gives well defined signals which helps with structural interpretation

abundant isotope - H1 is way more abundant than H2 or D

highly receptive // how sensitive it isif all other parameters are the same

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2
Q

what do we use as a referance in nmr

A

tetramethylsilane , SiMe4 TMS

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3
Q

what chemical shift does TMS have

A

its said to have a precession frequency, but the chemical shift is said to be 0.

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4
Q

what is the typical ranges of A CHEMICAL SHIFT in nmr spectrum

A

0-10 ppm

majority of compounds are found in this region.

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5
Q

H2 is also known as

A

deuterium

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6
Q

what type of solvent do we use in H1 nmr // general

A

we use deuterated solvents - solvents where most of the H’s are H2 (99.6%),, which are invisible in H1 nmr spec.

some contain inpurities (some H1) which shows up as an impurity signal.

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7
Q

give a deuterated solvent example and their impure versions.

A

CDCl3 = CHCl3
C6D6 = C6D5H

the H1’s will give a visible impure signal

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8
Q

why do we need to use a deuterated solvent

A

bc normally in a sample,, there are more H1’s in the solvent than the analyte.

meaning the sample will be analysed.

we use deuterated solvents so that only the H1’s are analysed by H1 nmr.

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9
Q

in CHDCl3,, what will the H couple to

A

it will couple to the deuterium.
which has a spin of (I=1)

and then 2nI+1 -> 3
so the impurity will be a triplet

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10
Q

the closer the electronegative group,,

A

the more e- it attracts,, the less shielded the H is,, the larger precession frequency it has,, the larger the chemical shift it has

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11
Q

order Ch, CH2 and CH3 in terms of which one has the greater chemical shift

A

CH
CH2
CH3

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12
Q

what are the effects of a functional group

A

theyre additive
so u have to add the effects of both fg and their effects to the chemical shift values

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13
Q

aldehyde chem shift

A

10ppm

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14
Q

benzene chem shift

A

8ppm

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15
Q

alkene chem shift

A

6ppm

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16
Q

heteroatom on same C to the H were measuring chemical shift

A

4ppm

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17
Q

heteroatom on adjacent c to the H that were measuring the chemical shift of

A

2ppm

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18
Q

normal alkane

A

1ppm

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19
Q

alcohol chemical shift range

A

5-2 ppm

20
Q

why is the alcohol chem shift range so large

A

It has hydrogen bonding

H bonds are affected by concentration,,

diff conc = diff num of Hbonds = diff shielding = diff precession frequency = diff chemical shift

different conc = diff chemical shift = diff Hbonds

21
Q

how can we accurately measure the chemical shift of smt when if may have H bonds

A

DTO shake.

deuterium exchanges protons of OH to D,, no more H bonds,, invisible to H1 NMR spectra + the alcohol peak is removed from the H1 nmr spectrum.

22
Q

what is OH bonding affected by

A

temp
concentration

23
Q

diff temp with OH bonding

A

diff temp = diff H bonds = diff chemical shift

24
Q

diff conc with OH bonding

A

higher conc = more Hbonds = diff shielding = diff chemical shift.

25
Q

more shielded =

A

lower chemical shift
more e- to protect proton from EMS

26
Q

what increases from right to lect on an nmr specta

A

the energy of the radiofrequency radiation

27
Q

energy of radio frequency radiation on the rhs of the h1 nmr spectra

A

low energy RFR

28
Q

energy on the lhs of the h1 nmr spectra

A

high radio frequency radiation

29
Q

position of the signal on nmr spectrum is proportional to what

A

the radiofrequency radiation

30
Q

when all arrows arrows are pointing up,, how is the applied magnetic field affected

A

when theyre all up,, aligned with it,, they strengthen the applied magnetic field

more precession,, higher chemical shift

31
Q

what is integration

A

area under the curve

relative to the amount of protons that give that signal // indicates the relative number of hydrogen atoms.

32
Q

how do we find integration

A

area under peaks

height of integration curve in mm / height of the smallest integration curve in mm!!!

33
Q

symmetry has what kind of equilvalence

A

it has chemical equivalence

34
Q

what is chemical equivalence

A

when nuclei have the same chemical environment

the nucs with the same chem environment have the same proximity to other nuclei in the molecule

35
Q

what is magnetic equivalence

A

requires nuclei to have identical coupling partners.

identical chemical shifts
identical coupling constants
identical coupling partners

36
Q

lowkey trick to see magnetic equivalence

A

see if one of the H’s has other H’s next to it

2 H’s,, are they magnetically equivalent?
do one of them have more H’s next to it?? aka are they coupled to 2 diff things

yes? -> probs not magnetically equivalent

no? -> probs magnetically equivalent.

37
Q

how to think of magnetic equivalence

A

marriage + couples

if they are diff couples –> theyre not married aka they dont have magnetic equivalence.

38
Q

what is 3 bond coupling

A

when the things that are coupled are 3 bonds apart

39
Q

what is 4 bond coupling

A

when the things being coupled are 4 bonds apart

40
Q

the larger the bond coupling theee

A

the smaller the magnitude = the smaller the hz

41
Q

are molecules flat

A

nope

42
Q

what is topicity

A

the sterochemical relationship between 2 apparently identical groups.

43
Q

what does homotopic mean

A

when the moelcule is rotated,, it turns out to tbe the same

44
Q

what does enantiotopic mean

A

enantiomers of eachother,,, identical signals in nmr.

not the same tho!! their wedges and dashes will be different. one will be r and one will be s

45
Q

what does diastereotopic mean

A

2 chiral centres
different nmr signals
one of the chiral centres will switch!!

year 2 spec (8 decks)

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