chapter 17

• In a mass spectrometer, a compound loses an electron to form a positive ions called the molecular ion. The mass to charge ratio of the molecular ion gives the spectrum
• The M+ peak is the clear peak at the highest mz value on the right hand side of the spectrum, which shows the molar mass. The m+1 peak exists because there is 1.1% of carbon is present as the carbon13 isotope
• In a mass spectrometer, some molecular ions break down into fragment ions in a process called fragmentation. The simplest fragmentation breaks down into fragment ions and radicals
• Common fragment ions:

  Ch3 - 15

  C2H5 -29

  Ch2OH- 31
• There are two types of vibrations when bonds absorb infrared radiation:

  Stretch and bend
• The amount a bond stretches and bends depends on the mass of the atoms and the strength of the bond
• chemists use infrared spectroscopy to identify the functional groups present in organic molecules

  A beam of 200-4000cm-1 is passed through the sample and the IR spectrometer identities the frequencies absorbed by the bonds
• Below 1500 is called the fingerprint region which is used to identify the particular molecule under investigation
• Common bond wave numbers

  O-H (alcs)- 3200-3600

  O-H(carbs)- 2500-3300

  C=O( carbonyl)- 1630-1820
• Alcohols have one peak big peak at 3200-3600

  Carbonyl groups have a skinny deep peak at 1630-1820

  Carboxylic Acids have a broad deep peak at 2500-3330 and a skinny deep peak at 1630-1820
• Infrared spectroscopy is also used to detect vehicle emissions and for breathalysers to detect drink driving
• A typical sequence for identification:

  Elemental analysis

  Mass spectrometry

  Infrared spectroscopy