U1 Drug Analysis Flashcards
What is NMR?
What is the function of the magnet controller in NMR?
nuclear magnetic resonance
stimulate the resonance of specific nuclei; nuclei with odd numbers
What are the common nuclei used in NMR?
What is special about them?
H1, C13 etc
spin and charge of nuclei means they act like magnets
What is the nuclei resonance detected as?
radio wave signals
What determines the position where a nucleus resonates?
- exact magnetic environment
- somewhat determined by electronic environment nearby ie. nearby atoms
What is electronegativity?
ability of an atom to attract electrons
How does electronegativity of an atom affect its chemical shift on an NMR?
the more electronegative, the higher the shift e.g. Fluorine most electroneg halide; shifts to 4
e.g. CH2Cl2 shifts to 5.30
CHCl3 shifts to 7.27
chemical shift units on NMR
delta ppm
electron withdrawing groups are described as what on NMR?
What effect do they have?
deshielding
movement to a higher delta - DOWNFIELD (towards 12)
What happens if electron density is increased? ie presence of electron donating group
nuclei is ‘shielded’
move delta upfield (towards zero)
What functional groups can you expect to see from zero to three?
alkyl
alkyne
What functional groups would you expect to see in 5/6?
alkenes
Where would you expect to see aromatics?
7/8
Where would you expect to see carbonyls?
9-12
e.g. aldehyde 9/10
COOH 10/12
Where would you expect to see hydroxyls (-OH) and amines (-NH2)?
Why is the variation in chemical shift so big?
1-6
presence of H bonding
What is the proton NMR scale?
0-12
What is the 13C NMR scale?
0-250
What is integration in regards to proton NMR?
used to quantify the relative number of protons contributing to each system in the spectrum
What is the area under a proton NMR peak proportional to?
the number of hydrogen atoms represented by the peak
the size of the jumps ie the difference between peaks on proton NMR spec is proportional to what?
number of Hs
What are splitting patterns on proton NMR determined by?
What is the rule?
number of adjacent protons
n+1
where n = number of adjacent protons
What will the splitting pattern be if there are no adjacent protons?
1, singlet
What will the splitting pattern be if there is 1 adjacent proton?
What will the relative intensities be?
2 peaks, doublet
1:1
What will the splitting pattern be if there are 2 adjacent protons?
What will the relative intensities be?
3, triplet
1:2:1
What will the splitting pattern be if there are 3 adjacent protons?
What will the relative intensities be?
4, quartet
1:3:3:1
What is meant by ‘coupling’ ?
refers to the interaction between neighboring nuclear spins, which results in the splitting of NMR signals into multiple peaks
What splitting pattern can be seen in monosubstituted arenes?
- usually split into 2 groups
- those closest to monosubstitution
- those further away - peaks in ratio 2:3 or 3:2
With aromatics, what factor is arguably more influential on the delta value than electronegativity?
the substituent on the ring
What is the effect on NMR spec of adding an electron donating group as the substituent on the ring?
- adds to conjugated system, shields aromatic proteins
- shift upfield
What sorts of groups are electron donating?
amine, OH, amides, OR, aryl, alkyl (strongest to weakest)
What groups are considered electron withdrawing?
all carbonyls (electron deficient carbon), nitriles, nitro
