organic analysis Flashcards
what can be used to identify the particular isotope
high resolution mass spec
how many decimal places does HRMS go to
0.0000
advantages of HRMS
narrow down compounds
disadvantages of HRMS
cant identify specific species
what can IR spec be used to identify
technique used to identify compounds based on changes in vibrations of atoms when they absorb IR of certain frequencies
how does IR spec work
A spectrophotometer irradiates the sample with electromagnetic waves in the infrared region and then detects the intensity of the wavelength of IR radiation which goes through the sample
All organic molecules absorb IR radiation and depending on which energies of radiation are absorbed, bonds between atoms will vibrate by stretching, bending and twisting
The molecules will only vibrate at a specific frequency
what does the specific frequency generate for each molecule
-a fingerprint region
-functional group signals
what are the units of IR spec
This unit is called the wavenumber (cm-1)
what is the fingerprint region
-below 1500 cm-1
-specific to each compound
-although harder to identify specific func groups
-can check is compound is pure- compare against known- any extra peaks show an impurity
-to identify compound u ignore this region
what do u look at to identify func group
func group region - above 1550 cm-1
what values do u use
values on data sheet
what is the wavelength of C-H bonds on C atoms that are saturated
below 3000cm-1
what is the wavelength of C-H bonds on C atoms that are unsaturated - double bonds
above 3000cm-1
O-H alcohols
smooth peak - usually no C-H overlap
O-H acid
jagged/ broad - overlap with C-H
C=O
narrow and strong
C=C
small but check for C-H above 3000 for confirmation
C-N
small but jagged around 3000
how does HRMS work
-The molecules in the small sample are bombarded with high energy electrons which can cause the molecule to lose an electron
-This results in the formation of a positively charged molecular ion with one unpaired electron
-One of the electrons in the pair has been removed by the beam of electrons
-The molecular ion can further fragment to form new ions, molecules, and radicals
These fragmented ions are accelerated by an electric field
then detected
very similar to ionisation in atomic structure
how do the ion fragments seperate
Based on their mass (m) to charge (z) ratio, the ion fragments are then separated by deflecting them into the detector
Most ions will only gain a charge of 1+ and therefore a ion with mass 12 and charge 1+ will have an m/z value of 12
It is, however, possible for a greater charge to occur. For example, an ion with mass 16 and charge 2+ will have a m/z value of 8
HRMS of chlorine and its isotopes
For example, Cl-35 and Cl-37 are isotopes as they are both atoms of the same element (chlorine, Cl) but have a different mass number (35 and 37 respectively)
Mass spectroscopy can be used to find the relative abundance of the isotopes experimentally
The relative abundance of an isotope is the proportion of one particular isotope in a mixture of isotopes found in nature
For example, the relative abundance of Cl-35 and Cl-37 is 75% and 25% respectively
This means that in nature, 75% of the chlorine atoms is the Cl-35 isotope and 25% is the Cl-37 isotope
The heights of the peaks in mass spectroscopy show the proportion of each isotope present
