Structure of molecules

• what is the structure of allenes?

  twisted
• what is x-ray diffraction?

  Analyzing crystal structure
• what is an issue of x-ray diffraction?

  may take several day

  only works with crystals
• what techniques are used to determine structure?

  mass spec

  IR

  NMR

  x-ray
• what does mass spec do?

  weigh molecule - gives molecular formula

  must be positively charged particle
• what is a double bond equivalent?

  measure of how unsaturated a carbon is
• what is 1 DBE?

  ring system

  double bond
• how to calculate DBEs?

  Cn (2n + 2) -H /2

  CnNm (2n + 2 + m) -H /2
• what does infra-red require?

  bonds that can vibrate
• what appears a high wavelength on infra-red?

  strong bond - vibrate quickly
• what appears between 4000-2500 on infra red?

  O-H

  N-H

  C-H
• what appears between 2500-2000?

  C triple bond C

  C triple bond N
• What appears between 2000-1500 in infra red?

  C=O

  C=C
• what appears between 1500-500?

  C-O

  C-F

  C-Cl
• where do C-H stretch in infra red?

  3000cm

  but with alkynes are intense sharp peaks at 3300cm
• how many peaks appear on a infra red peak for a NH?

  2, due to stretching shape (symmetric - 3300, antisymmetric - 3400)
• why do alcohol form a broad peak?

  average of hydrogen bond network
• where is the fingerprint region?

  1500-500
• where do c=c bonds appear in infra red?

  1640
• where does acyl chloride come in infra red?

  1800
• where does ester come in infra red?

  1740
• where does aldehyde come in infra red?

  1730
• where does ketone come in infra red?

  1710
• where does carboxylic acid come in infra red?

  1710
• where do nitro group come in infra red?

  1560 - 1350, antisymmetric 1550, symmeteric = 1350
• what does polarity of bond affect ?

  more intense ir peak