Topic 7: Modern Analytical Techniques Flashcards
Where can you find the molecular ion peak (mass spectrometry)
Peak furthest right
What is the molecular ion peak a result of? (Mass spectrometry)
The organic molecule losing an electron in the mass spectrometer eg. C3H6O+
(An electron will collide with the molecule eg. Butane and knock out an electron)
What is the M+1 peak referring to and why does it appear
Very small peak just to the right of the molecular ion peak
Caused due to presence of a naturally occurring isotope of carbon
What are peaks with smaller m/z values a result of?
Fragmentation (occurs when molecular ion breaks into smaller pieces)
Two species are formed : another positive ion and a neutral species (usually a radical)
Radicals are not detected in the mass spectrometer so all peaks formed are caused by positive ions
How are the peaks formed by fragmentation determined? (Mass spectrometry)
Depends on how the carbon-carbon bond breaks
If the molecule is symmetrical only one peak is formed due to fragmentation
If not there will be more than one possible fragment ion and therefore you would expect to see more than one peak
What does the tallest peak represent (mass spectrometry)
The ion with the highest abundance (most stable fragment)
Often referred to as the base peak
What are two possible effects when IR is absorbed by molecules ?
Stretching- bond length increases & decreases
Bending- bond angle increases & decreases
How is the axis usually labelled in mass spectrometry
Vertical axis: relative intensity (%) 0-100
Horizontal axis: m/z 0-just beyond molecular ion peak
How is the axis usually labelled in IR spectroscopy
Vertical axis : Transmittance (%) 0-100
Horizontal axis : wavenumber (cm-1) 4000-500
What are the dips or troughs of an IR spectrum referred to as?
Absorptions (sometimes peaks)
How can we describe characteristic absorptions
Look at the table in the data booklet
Can describe as either sharp/broad absorption
We can also comment on a missing absorption
