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 original molecule that hasn’t fragmented, known as the molecular ion
• Why is the mass/charge ratio equal to Mr in mass spectrometry?


  Because the charge of the ion is +1
• What is the molecular formula of butane?


  C4H10
• How is the molecular ion formed in mass spectrometry?


  By knocking off one electron from the molecule
• What is the significance of high resolution mass spectroscopy measuring mass to 5 decimal places?


  It helps differentiate between compounds that appear to have similar Mr
• What is the accurate mass of hydrogen?


  1. 0078
• What is the accurate mass of carbon?


  12.0000
• What is the accurate mass of oxygen?


  15.9949
• What is the accurate mass of nitrogen?


  14.0031
• Given an Mr of 60.02112, what is the molecular formula?


  C2H4O2
• Given an Mr of 60.05751, what is the molecular formula?


  C3H8O
• Given an Mr of 60.03235, what is the molecular formula?


  CH4N2O
• How do you calculate the Mr of CH3CH2OH?


  By using the formula: $(12.0000 \times 2) +$$(15.9949 \times 1) +$$(1.0078 \times 6) =$$46.0417$
• How do you calculate the Mr of H2NCH2NH2?


  By using the formula: $(12.0000 \times 1) +$$(14.0031 \times 2) +$$(1.0078 \times 6) =$$46.0530$
• 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 m/z value of CH3Cl?


  M is 50 and M+2 is 52
• What is the ratio of heights for CH3Cl's M:M+2 peaks?


  1. 1
• What is the m/z value of CH3Br?


  M is 94 and M+2 is 96
• What is the ratio of heights for CH3Br's M:M+2 peaks?


  1. 1
• What is the m/z value of C2H4Cl2?


  M is 98, M+2 is 100, and M+4 is 102
• What is the ratio of heights for C2H4Cl2's M:M+2:M+4 peaks?


  1. 6:1
• What is the m/z value of C2H4Br2?


  M is 186, M+2 is 188, and M+4 is 190
• What is the ratio of heights for C2H4Br2's M:M+2:M+4 peaks?


  1. 2:1
• What is the m/z value of C2H3Cl3?


  M is 132, M+2 is 134, M+4 is 136, and M+6 is 138
• What is the ratio of heights for C2H3Cl3's M:M+2:M+4:M+6 peaks?


  27:27:9:1
• What is the purpose of infrared spectroscopy?


  To absorb infra-red radiation at characteristic frequencies
• What is the fingerprint region in infrared spectroscopy?


  Below 1500 cm-1, unique for every 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 wave number range for the C=O bond in infrared spectroscopy?


  1680 – 1750 cm-1
• What is the wave number range for the O-H bond in acids in infrared spectroscopy?


  2500-3000 cm-1
• What do "rogue" absorptions indicate in infrared spectroscopy?


  They are indicators of impurities
• How does the absorption of infrared radiation contribute to the greenhouse effect?


  C=O bonds in CO2 absorb infrared radiation, preventing it from escaping the atmosphere
• 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 reaction with aldehydes?


  • Reagent: Formed by mixing aqueous ammonia and silver nitrate
  • Active substance: Complex ion of [Ag(NH3)2]+
  • Conditions: Heat gently
  • Reaction: Aldehydes oxidized to carboxylic acids; silver(I) ions reduced to silver atoms
  • Observation: Silver mirror forms with aldehydes; no change with ketones
• What is Fehling’s Solution and its reaction with aldehydes?


  • Reagent: Contains blue Cu²⁺ ions
  • Conditions: Heat gently
  • Reaction: Aldehydes oxidized to carboxylic acids; copper(II) ions reduced to copper(I) oxide
  • Observation: Blue Cu²⁺ ions change to red precipitate of Cu₂O; ketones do not react
• How can the presence of a carboxylic acid be tested?


  • By adding sodium carbonate
  • Result: Fizzing and production of carbon dioxide
• What is the mechanism of the greenhouse effect?


  • UV radiation passes through the atmosphere and heats the Earth
  • Earth radiates infrared radiation
  • C=O bonds in CO₂ absorb infrared radiation, preventing it from escaping
  • Energy is transferred to other molecules, warming the atmosphere