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Infrared Spec
Alcohols
Acids
Ketones
Amines
measure molec vibrations: stretching, bending and rotations Best to identify functional group Alcohols - broad peak 3100-3500 Acids - broadest - C=0 and O-H Ketones - sharp Amines- sharp
Why does O-H group have broad peak in IR
The variable pull on H changes the apparent mass of H atom - this is stretching.
How to determine how many signals in C-NMR?
number of different Cs in the compound. Different means different things attached to it. Eg benzoic acid has 5
torisional strain
occurs between atoms on same compound. Caused by repulsion between electrons/bonds when atoms are close
staggered vs eclipsed
staggered, groups on adjacent C as far apart as possible.
eclipsed - as close as possible
gauche
staggered but eg 2 methane groups are close (like at 12 and 2)
anti
staggered, like mthane groups at 12 and 6
SN1
Rate can never be more than rate determining step
LG leaves, making carbocation
nuc attacks
rate only depends on the conc or original mcule bc it’s the only reactant
Best in polar and protic solvents eg water and alcohol
Will usually give a racemic mixture because of the planar carbocation!
SN2
nuc attacks and Lg leaves ONLY 1 step depends on conc of both strong nuc attack from back polar aprotic solvents Why not protic? Because H would bond to nuc and stop it from attacking, remember we need the nuc to be really strong in sn2 bc it has to force the lg to leave
When will Sn1 happen over sn2?
Tertiary>2>1>methyl
planar
achiral
SN2 over SN1?
methyl>1>2>3
chiral transition state
rxn flips the bonds
Great LG
weak bases, halogens
Strong nucs
strong bases, larger is better
RO->HO->RCO2->ROH>H2O
Elimination rnx
alkane - alkene via removal of halide or OH
E1 How many steps rate determining step mech favorable conditions
Unimolecular elim.
2 steps carbocation intermediate like sn1
only conc of substrate matters
LG leaves eg Cl
weak nuc (OH-) pulls H off of other C, makes alkene
polar, highly sub C groups, weak nuc
E2
bimolec elim
1 step like sn2
conc of substrate and base (strong nuc!)
Strong nuc plucks off H, halide (LG leaves too)
NB! Goes after more substituted C so that double bond is somewhere in the middle of the cpound instead
enantiomer
isomers that are mirror images
structural isomer
same molec formula
geometric isomer
same atoms, bonds, different spatial arrangement
ortho, meta, para
ortho - adjacent 1,2 position
meta - 1,3 poisition
para - 1.4
THINK PARa = even out
solubility inc or dec with Temp?
dec
think heating mixes things up
IR spec - what does a high peak mean?
it means there is more of that particular group relative to others in the sample
but it’s not quantifiable, like don’t use IR to figure out concentrations of a group in a sample
what is the best way to decipher an unknown in large quantities?
extraction
identify unknowns on small scale?
you can use gas chromatography
paper chrom
mass spec
