12: Spectroscopic Analysis of Organic Compounds Flashcards
How does Infra-red Spectroscopy work
Molecules absorb infra-red radiation
The energy absorbed causes the covalent bonds in the covalent bond in the molecule to vibrate
Vibrations are measured
What wavenumber region is the finger print region
1500 - 0 cm¯¹
Should you try to interpret the fingerprint region
No
How to find the molecular ion peak in mass spectrometry
The peak furthest to the right (excluding the m+1 peak)
What does the m/z of the molecular ion peak equal
The Mr of the compound
What do you need to remember when writing fragment ions
They have a positive charge
What does the number of peaks in a ¹³C NMR spectrum equal
The number of carbons with different environment in the molecule
If carbons are equivalent due to symmetry how many peaks do they produce
Only 1
What are the units of chemical shift, δ
parts per million (p.p.m.)
What substance is used to create a reference peak
Tetramethylsilane (TMS), Si(CH₃)₄ which is set at 0ppm
What is the area under the peak in ¹H proportional to
The number of Hs contributing
Not necessarily the actual number as is it is shown as a ratio
eg. if one peak was due to 4 protons and and another due to 2 protons, the areas could be 4:2 or 2:1
What does the number of splittings depend on
The number of Hydrogens attached to the adjacent carbon(s) + 1
What is the name of a peak that is not split
singlet
What is the name of a peak that is split into 2
Doublet
What is the name of a peak that is split into 3
Triplet
