Topic 7.1 Analytic Techniques

The mass spectrum of an element often appears very simple, with a very small number of vertical lines, called peaks, each one representing an isotope of the element.

The mass spectrum of inorganic compound often appears complex, with a large number of peaks

-The peak furthest to the right on the mass spec of an organic compound. -greatest m/z value (mass to charge ratio)/ -It is the result of an organic molecule losing an electron(an electron collides with a molecule and knocks out an electron, so forming a positive ion). -The m/z value of this peak indicates the relative molecular mass.

The very small peak just to the right of the molecular ion peak. This is caused by the presence of carbon in the molecule.

The peaks with smaller m/z values result form fragmentation in the mass spectrometer, rearrangement reactions and the loss of more than on electron. (Rearrangement is often unpredictable).

Fragmentation is very common and can often be used to work out the structure of an organic molecule. Consider the breaking of a carbon-carbon bond in the molecular ion formed from a hydrocarbon. Two species are formed: -another positive ion -a neutral species (usually a radical)

• Consider possible techniques that have a molecular formula C3H8O • Look at the unique peaks • Which molecule(s) have a structure that can fragment to create that ion peak

Butane CH3CH2CH2CH3 29 peak: [CH3CH]+ 43 peak: [CH3CH2CH2] 58 peak: [CH3CH2CH2CH3]+

Bromomethane CH3Br 15 peak: [CH3]+ 94 peak: [CH3 79^Br]+ 96 peak: [CH3 81^Br]+

Infrared is a simple, quick method that both confirms which organic functional groups are present in the test compound and those that are not.

-Which peak on the spectrum you are referring to by their value -Which feature in the structure is/is not present

-Picking out functional group signal is difficult -This part of the spectrum is unique for every compound, and so can be used as a ‘fingerprint’ -This region can also be used to check if a compound is pure (A distinctive characteristic or pattern indicating the presence of a certain molecule).

primary alcohols [O]–> aldehyde [O]–> carboxylic acid secondy [O]–> ketone tertiary can’t no space to form double bond with O