by rigel


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High Rf on a TLC plate means
  • lower polarity of spotted compound
  • changing polarity of solvent will not change this, will just increase Rf values across the board
IR Spectroscopy trends and values for:
  • Carbonyl
  • NH
  • OH
  • fingerprint region
Electronegative or electron withdrawing substituents will reduce the frequencies here
  • carbonyl carbons have strong bands around 16500-1720 cm-1 and if on a carbocylic acid the extra OH resonance brings it to the top end of that. Cl on the same C brings it up a bit further.
  • NH has a strong band around 3300-3600 cm-1
  • OH has a broad band around 3400 cm-1 but if its part of a carboxylic acid the resonance brings it way down to 2500-3000
  • 800-1400 is fingerprint
Mass spec
  • m/z (mass to charge) ratio
  • molecular ion peak
Organometallic reagent reactions with Aldehydes and ketones

Wolff-Kishner rxn
uses hydrazine to reduce ketone or aldehyde to an alkane, with evolution of N2
  • Hoffmann rearrangement of acid derivatives
  • Hoffmann elimination of amines
  • reaction of a primary amide to a primary amine with one fewer C atom.
  • Amine + MeI + AgO2 -> alkene + tertiary amine. With unsymmetrical amines, the major alkene product is the least substituted and generally the least stable, an observation known as the Hofmann rule.
Reaction of amines with nitrous acid
Nitrous acid (HONO) is prepared in situ from NaNO2 and sulfuric acid
  • primary amines give off N2 gas from clear solution
  • secondary amines form yellow nitrosamine oil
  • tertiary amines form quaternary ammmonium salt, no gas
NMR shifts
proximity to an electronegative element or electron withdrawing group will shift signal downfield (to left)
aldol condensation
one enol or enolate (carbonyl) compound adds to alpha carbon of another carbonyl carbon to form a alpha, beta aldol
haloform rxn
replacement of methyl hydrogens by halogens in presence of base or acid catalysis. tri-halogenation results in an oxication to carboxylic acid and production of a haloform (HCX3)
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