Spec

• Chromophore


  the structural feature able to absorb UV/vis radiation

  UV: 200-330 nm vis: 330-700 nm
• Quadrupolar nuclei - I >1/2
• Strong coupling - occurs when the change in delta approaches the coupling constant (J)

  • multiplet intesities are distorted (roofing)
  • centres of multiplets may not represent
  • splitting may not represent the true coupling constants
  • spectra is harder to interpret
• Inductive effects - dipoles - nuclear shielding

  short range

  electronegative groups - deshield the nucleus

  electropositibe groups - shield the nucleus
• Mesomeric effects - resonance structures
• Anisotrpic effects

  • arise from asymmetry of electron density in bonds
  • common in unsaturated systems
• Anisotrpic effects

  • arise from asymmetry of electron density in bonds
  • common in unsaturated systems
  • produces ring currents (circulating pi electrons)
  • produces strong deshielding effects
• 𝛍 = 𝛄I

  𝛍: magnetic dipole moment

  𝛄: magnetogyric ratio

  I: spin angular momentum (spin quantum number)
• Mass spec resolution - R = m/𝚫m

  R: resolution

  m: the mass to be measured

  𝚫m: the separation of masses (peak width)
• High resolution MS

  • high resolution + accuracy
  • small error margin
• EI: electron impact ionisation

  CI: chemical ionisation (in the gas phase)

  • less energy is transferred - less fragmentation
  • the specra produce is not reproducable
  • pressure of CI gas is variable
• IR spec

  • stretching - high energy
  • bending - lower energy
  • double and triple bonds absorb at higher frequencies (energies)
  • small atomic masses absorb at higher frequencies
  • absorption is quoted in wavenumbers (v)
• IR spec

  • stretching - high energy
  • bending - lower energy
  • double and triple bonds absorb at higher frequencies (energies)
  • small atomic masses absorb at higher frequencies
  • absorption is quoted in wavenumbers (v)
  • the number of wavelengths per cm
• IR regions - more conjugation = lower wave number

  fingerprint region: < 1500

  C=C: 1600-1700

  C≡C: 1900-1500

  O-H: 3000 BROAD (H-bonding)

  N-H: 3300-3500

  C-H: 3000

  S-H - 2550-2600