Topic 7- MASS SPEC AND INFRARED

• Mass spectrometry

  Technique that ionises molecules and then detects and measures the mass-to-charge ratio (m/z) of the resulting ions
• Infrared spectroscopy


  Technique that measures the absorption of infrared radiation by a sample, which can provide information about the molecular structure
• Ionisation in mass spectrometry

  • Only particles with a positive charge will be deflected and detected
• Molecular ion

  When a molecule is ionised it forms a molecular ion, which can break up to produce particles of smaller mass
• Mass spectrum

  The sample is vapourised, ionised (by e- bombarded, which turns the molecule into ion by knocking out an e-). The ion is then accelerated, deflected in a magnetic field (high vacuum) and detected---to produce +ve charged ions and fragments.

  
• Molecular ion peak

  The highest m/z value usually corresponds to the molecular ion, and its position provides information about the molecular mass of a substance
• The tallest peaks come from the most stable species
• The small peak (M+1) at 115 is due to the natural abundance (about 1%) of carbon-13
• Fragmentation in mass spectrometry

  • Peaks appear due to characteristic fragments
  • Peaks can occur at m/z values corresponding to the ions produced by breaking C-C bonds
  • The more stable the carbocation formed, the more abundant it is (and the higher the peak)
• IONISATION IN MASS SPECTROMETRY (does not involve radiation)

  A) molecular

  B) break

  C) smaller

  D) positive ion

  E) free radical

  F) positive

  
• THE MASS SPECTRUM

  A) fragment

  B) molecular

  C) mass

  D) stable

  
• EXAMPLE GRAPH AND SPLIT INTO FRAGMENTS AND MOLECULAR ION

  A) fragment

  B) molecular ion

  C) Mr

  D) +CH2CH3

  E) + e-

  
• EXAMPLE OF MASS SPECTRUM (OCTANE )

  A) BASE

  B) abundant

  C) stable

  D) highest

  E) C-13

  
• EXAMPLE MASS SPECTRUM- FRAGMENTATION OF OCTANE

  A) CH3CH2+

  
• MASS SPECTROMETRY-Fragmentation

  A) e-

  B) +ve

  C) radical

  D) positive

  E) CH3+

  
• INFRARED SPECTROSCOPY---has radiation. Carboxylic acid spectrum with C double bond O and O-H

  A) fingerprinting region

  B) functional

  C) convalent

  D) vibrate

  E) unique

  
• INFRARED SPECTROSCOPY v=frequency

  A) hv

  B) light

  C) wavenumber

  
• Infrared spectroscopy

  A) heating

  B) absorb

  C) infrared

  D) e- exitement

  E) translational

  F) vibrate

  G) absorb

  
• Infrared spectroscopy- the frequency of vibration depends on:


  atom size, bond length and bond strength
• Types of vibration

  symmetric, asymmetric, wagging, twisting, scissoring, rocking

  
• For a molecule to absorb IR radiation, the vibration must involve a change in the dipole moment of the molecule. 


  POLAR MOLECULES- all absorb IR radiation in all their bending/stretching modes NON-POLAR- absorbtion depends on weather or not bonds are polar

  A) moment

  B) than 0

  C) absorbs

  D) change

  E) polar

  F) non polar

  
• The IR spectrometer measured the amount of IR radiation absorbed by the molecule for a range of frequencies

  measures the amount of IR absorbed, measure the frequency of absorption

  A) solvent

  B) dissolved

  C) detector

  D) beam