Organic Analysis Flashcards
What is the infrared spectroscopy theory?
A technique which can be used to identify the functional group present in an organic molecule
Infrared energy is absorbed by bonds which can make the bonds vibrate. the bonds vibrate at the same frequency as the infra red energy.
Describe the process of IR spectrometer
- A beam of IR light containing a wide wangle of frequencies is passed through a sample.
2.Some of the frequencies of IR light are absorbed by the molecule. Many of the frequencies are not absorbed so pass straight through the sample. The light that emerges through the other side of the sample is missing the frequencies which are absorbed - Once detected, a computer plots the graph off the intensity of the light- this is transmittance
What are the peaks on the spectra called?
What does a C=O bond represent
The spectrum represents a ketone because it has an absorption matching the C=O bond from 1680-1750 cm-1
How are alcohols and carboxylic acids determined
OH alcohol bond looks like a test tube- carboxylic looks like a jagged point.
Why would the spectrum represent a ketone and not a carboxylic acid
Because it has an absorption range matching the C=O bond from 1680-1750 but no OH peak
What is the fingerprint region
The area of the spectrum that is 1500cm-1 and below
Why would a person not be able to use the IR spectrum to determine the difference between propan-1-ol’ and propane-2-ol
They both have the same absorption for the OH bond
How can mass spectrometry be used to confirm that a compound is definitely ethyl butanoate
Compare with a known spectrum from a data base, it should be an exact match
What two factors does mass spectrometry measure
The relative abundance and the mass:charge ratio
Electron impact
High energy electrons fired out of an electron gun at sample. Knocks off an electron so gains a positive charge
Electrospray
Sample is dissolved in volitile solvent and passed through a fine needle at high voltage. Each molecule gains a proton and a positive charge
How do you find the mr from a mass spectrometry peak
The peak with the largest mz is equal to the mr of the molecule
This peak is called the molecular ion peak
To what decimal place does each spectrometry measure
Mass spectrometry measures to 1 do
Hugh resolution mass spectrometry measures up to 5 decimal places
Why can’t a mass spectrometer which measures m/z ration be able to tell the difference between C10H16O4 and C11H4O4
Both substances have the same mr to one decimal place
