Organic analysis

• What can high resolution mass spectrometry determine from the accurate mass of the molecular ion?

  The molecular formula of a compound
• What does the peak with the highest mass/charge ratio in mass spectrometry represent?

  It represents the molecular ion that hasn't fragmented
• What is the molecular formula of butane?

  C4H10
• What is the molecular ion formed from butane?

  M → [M]+ + e–
• What is a molecular ion?

  It is the molecule with one electron knocked off, making it both an ion and a free radical
• How many decimal places can high resolution mass spectroscopy measure?

  It can measure the mass to 5 decimal places
• Why is high resolution mass spectroscopy useful for differentiating compounds?

  It helps differentiate between compounds that appear to have similar Mr to the nearest whole number
• What happens when a compound contains a chlorine or bromine atom in mass spectrometry?

  Two molecular ion peaks will occur: an M and an M+2 peak
• What are the naturally occurring isotopes of chlorine?

  Cl35 (75%) and Cl37 (25%)
• What are the naturally occurring isotopes of bromine?

  Br79 (50%) and Br81 (50%)
• What is the purpose of the fingerprint region in infrared spectroscopy?

  It is unique for every compound and can be used to identify the compound
• What is the significance of the region above 1500 cm-1 in infrared spectroscopy?

  It is used for functional group identification

  
• What is the wavenumber range for the C=O bond in infrared spectroscopy?

  1680 – 1750 cm-1

  
• What is the wavenumber range for the O-H bond in acids?

  2500 – 3000 cm-1

  
• What does a trough in the 1680-1750 cm-1 range indicate?

  It indicates the presence of a C=O bond
• What does a trough in the 2500-3000 cm-1 range indicate?

  It indicates the presence of an O-H bond in an acid
• What are the test-tube reactions for identifying functional groups?

  • Alkene: Bromine water → Orange colour decolourises
  • Aldehyde: Fehling’s solution → Blue solution to red precipitate
  • Aldehyde: Tollens’ reagent → Silver mirror formed
  • Carboxylic acid: Sodium carbonate → Effervescence of CO2 evolved
  • 1° 2° alcohol and aldehyde: Sodium dichromate and sulfuric acid → Orange to green colour change
  • Chloroalkane: Warm with silver nitrate → Slow formation of white precipitate of AgCl
• What is Tollens’ reagent and its use?

  Tollens’ reagent is formed by mixing aqueous ammonia and silver nitrate, used to oxidize aldehydes
• What happens when aldehydes react with Tollens’ reagent?

  A silver mirror forms coating the inside of the test tube
• What is the reaction equation for aldehydes with Tollens’ reagent?

  $CH3CHO +$$2Ag^+$$+$$H2O \rightarrow CH3COOH +$$2Ag +$$2H^+$
• What is Fehling’s solution and its use?

  Fehling’s solution contains blue Cu$^{2+}$ ions and is used to oxidize aldehydes
• What happens when aldehydes react with Fehling’s solution?

  Blue Cu$^{2+}$ ions change to a red precipitate of Cu$_{2}O$
• What is the reaction equation for aldehydes with Fehling’s solution?

  $CH3CHO +$$2Cu^{2+} +$$2H2O \rightarrow CH3COOH +$$Cu_{2}O +$$4H^{+}$
• How can the presence of a carboxylic acid be tested?

  By adding sodium carbonate, which will fizz and produce carbon dioxide
• What is the reaction equation for carboxylic acids with sodium carbonate?

  $2CH3CO2H +$$Na2CO3 \rightarrow 2CH3CO2^{-}Na^{+} +$$H2O +$$CO2$