TOPIC 7 - MODERN ANALYTICSL TECHNIQUES I + II

. Species formed from the molecule by the loss of one electron. e.g. C4H10 + e- —-> C4H10^+ + 2e- When an organic molecule loses an electron in the mass spectrometer- this can occur when an electron collides with the molecule, knocking out an electron so forming a positive ion.

A very small peak just to the right of the molecular ion peak. The naturally occurring isotope of carbon (carbon-13).

Molecular ion are energetically unstable breaks into smaller pieces: • Another +ve ion • A radical (neutral species) - does not show on mass spec as no charge and removed by vaccum pump. So all peaks caused by +ve ions • identical products of ethane = ch3+ + ch3 have same m/z = 15

mass/charge ratio (no. of e- lost) - indicates which ions are present, but height of peak indicates abundance. m/1 (normal) m/2 (halved) m/3 (third) • C=0 BONDS NEVER ALONE DO TO MASS SPEC NOT HAVING POLAR BONDS • CH2 NEVER ON ITS OWN • IF HAVE CARBOXYILIC ACID C=O-OH WRITE LIKE CHO+ • ALWAYS DRAW MOLECULE OUT TO HELP THEN SPLIT.

peak with the greatest abundance. = tallest peak most stable, common fragment

Similar molecules - used for carbon dating/half life as well

means the no.of peaks means the no of isotopes of that element. Determine peaks correspond to Br having 2 isotopes: [Br79 - Br79] + [Br79 - Br81]+ [Br81-Br79]+ [Br81 - Br81]+

Bonds between different atoms absorb different frequencies of IR radiation. POLAR BONDS SHOWN IN IR spec. That’s why polar bonds CO2, H2O and NO absorb IR - greenhouse gases - global warming. Non-polar molecules are NOT shown. A beam of IR radiation is passed through a sample of a chemical It is absorbed by covalent bonds in the molecules, increasing their vibrational energy causes effect on bonds like Stretching and bending. changes in vibration depend on frequency. High peak = high freq EM wave and radiates sample detects the intensity of wavelength of IR stretching - bond length increases and decreases. bending- bond angle increases and decreases. CAUSES DIPS IN THE GRAPH In the frequency absorbed, so OH groups on alcohols and carboxylic acids have different frequencies of absorption - SO LOCATION IS IMPORTANT. IR graph: y axis - Transmittance - value in an infrared spectrum that represents the amount of infrared radiation not absorbed (transmitted) at a particular wave number. 100% = NO ABSORPTION x axis - Wavenumber - 1/wavelength in cm - represents the frequency of the infrared radiation that was absorbed by a particular bond in a molecule H-BONDING CAUSES BROADNESS. HAVE NO H ATOMS = PEAK SHARPER.

• predict spectrum of organic compounds • deducing functional groups (polar bonds) • deducing structure from wave no. and molecular formula.

unique for each compound caused by absorption from bending. use to compare compounds and identify them