organic analysis

Question 1

what can be used to identify the particular isotope

Answer 1

high resolution mass spec

Question 2

how many decimal places does HRMS go to

Answer 2

0.0000

Question 3

advantages of HRMS

Answer 3

narrow down compounds

Question 4

disadvantages of HRMS

Answer 4

cant identify specific species

Question 5

what can IR spec be used to identify

Answer 5

technique used to identify compounds based on changes in vibrations of atoms when they absorb IR of certain frequencies

Question 6

how does IR spec work

Answer 6

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

Question 7

what does the specific frequency generate for each molecule

Answer 7

-a fingerprint region
-functional group signals

Question 8

what are the units of IR spec

Answer 8

This unit is called the wavenumber (cm-1)

Question 9

what is the fingerprint region

Answer 9

-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

Question 10

what do u look at to identify func group

Answer 10

func group region - above 1550 cm-1

Question 11

what values do u use

Answer 11

values on data sheet

Question 12

what is the wavelength of C-H bonds on C atoms that are saturated

Answer 12

below 3000cm-1

Question 13

what is the wavelength of C-H bonds on C atoms that are unsaturated - double bonds

Answer 13

above 3000cm-1

Question 14

O-H alcohols

Answer 14

smooth peak - usually no C-H overlap

Question 15

O-H acid

Answer 15

jagged/ broad - overlap with C-H

Question 16

C=O

Answer 16

narrow and strong

Question 17

C=C

Answer 17

small but check for C-H above 3000 for confirmation

Question 18

C-N

Answer 18

small but jagged around 3000

Question 19

how does HRMS work

Answer 19

-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

Question 20

how do the ion fragments seperate

Answer 20

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

Question 21

HRMS of chlorine and its isotopes

Answer 21

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