nmr 3

Question 1

why do we use H1 nmr aka proton nmrrr

Answer 1

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

Question 2

what do we use as a referance in nmr

Answer 2

tetramethylsilane , SiMe4 TMS

Question 3

what chemical shift does TMS have

Answer 3

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

Question 4

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

Answer 4

0-10 ppm

majority of compounds are found in this region.

Question 5

H2 is also known as

Answer 5

deuterium

Question 6

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

Answer 6

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.

Question 7

give a deuterated solvent example and their impure versions.

Answer 7

CDCl3 = CHCl3
C6D6 = C6D5H

the H1’s will give a visible impure signal

Question 8

why do we need to use a deuterated solvent

Answer 8

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.

Question 9

in CHDCl3,, what will the H couple to

Answer 9

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

Question 10

the closer the electronegative group,,

Answer 10

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

Question 11

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

Answer 11

CH
CH2
CH3

Question 12

what are the effects of a functional group

Answer 12

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

Question 13

aldehyde chem shift

Answer 13

10ppm

Question 14

benzene chem shift

Answer 14

8ppm

Question 15

alkene chem shift

Answer 15

6ppm

Question 16

heteroatom on same C to the H were measuring chemical shift

Answer 16

4ppm

Question 17

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

Answer 17

2ppm

Question 18

normal alkane

Answer 18

1ppm

Question 19

alcohol chemical shift range

Answer 19

5-2 ppm

Question 20

why is the alcohol chem shift range so large

Answer 20

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

higher conc = higher ppm = more deshielded

Question 21

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

Answer 21

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.

Question 22

what is OH bonding affected by

Answer 22

temp
concentration

Question 23

diff temp with OH bonding

Answer 23

diff temp = diff H bonds = diff chemical shift

Question 24

diff conc with OH bonding

Answer 24

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

Question 25

more shielded =

Answer 25

lower chemical shift more e- to protect proton from EMS

Question 26

what increases from right to lect on an nmr specta

Answer 26

the energy of the radiofrequency radiation

Question 27

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

Answer 27

low energy RFR

Question 28

energy on the lhs of the h1 nmr spectra

Answer 28

high radio frequency radiation

Question 29

position of the signal on nmr spectrum is proportional to what

Answer 29

the radiofrequency radiation

Question 30

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

Answer 30

when theyre all up,, aligned with it,, they strengthen the applied magnetic field more precession,, higher chemical shift

Question 31

what is integration

Answer 31

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

Question 32

how do we find integration

Answer 32

area under peaks height of integration curve in mm / height of the smallest integration curve in mm!!!

Question 33

symmetry has what kind of equilvalence

Answer 33

it has chemical equivalence

Question 34

what is chemical equivalence

Answer 34

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

Question 35

what is magnetic equivalence

Answer 35

requires nuclei to have identical coupling partners. identical chemical shifts identical coupling constants identical coupling partners

Question 36

lowkey trick to see magnetic equivalence

Answer 36

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.

Question 37

how to think of magnetic equivalence

Answer 37

marriage + couples if they are diff couples --> theyre not married aka they dont have magnetic equivalence.

Question 38

what is 3 bond coupling

Answer 38

when the things that are coupled are 3 bonds apart

Question 39

what is 4 bond coupling

Answer 39

when the things being coupled are 4 bonds apart

Question 40

the larger the bond coupling theee

Answer 40

the smaller the magnitude = the smaller the hz

Question 41

are molecules flat

Answer 41

nope

Question 42

what is topicity

Answer 42

the sterochemical relationship between 2 apparently identical groups.

Question 43

what does homotopic mean

Answer 43

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

Question 44

what does enantiotopic mean

Answer 44

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

Question 45

what does diastereotopic mean

Answer 45

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