NMR

Question 1

what is the standard molecule that peaks are measured against and give the structure

Answer 1

TMS (tetramethylsilane)
silicon with 4 methyl groups

Question 2

why do carbon environments have values that are shifted to the right

Answer 2

oxygen is very electronegative which changes the bond environment and how it absorbs energy

Question 3

what kind of solvent must samples be dissolved in for proton NMR and why

Answer 3

a non hydrogen containing solvent
so that it doesn’t produce any peaks on the spectrum

Question 4

name some solvents for proton NMR

Answer 4

CCl4
D2O
CDCl3

Question 5

what rule does the splitting pattern follow
give number of hydrogens on the adjacent carbon

Answer 5

‘n+1’ rule
singlet = no h on adjacent carbon
doublet= 1 h on adjacent carbon
triplet= 2 h on adjacent carbon
quarter= 3h on adjacent carbon

Question 6

what causes a nuclear spin

Answer 6

an atomic nucleus with an odd number of nucleons (protons and neutrons)

Question 7

what causes a weak magnetic field

Answer 7

odd number of nucleons in nucleus

Question 8

what happens when put in an external magnetic field

then a strong external force is applied

Answer 8

nuclei spin in random directions so their magnetic fields cancel out

then when strong external force is applied the nuclei will align with either the field or opposite to it

Question 9

what energy level are the nuclei aligned with the external field at

Answer 9

a slightly lower energy level than the opposed nuclei