Organic analysis.

Question 1

How many bonds are broken during fragmenation.

Answer 1

One bond is broken and it is usually the C-C bond.

Question 2

What is the highest fragmentation peak caused by.

Answer 2

The most stable species will cause this greatest peak - the carbocation.

Question 3

Define the molocular ion and give the species that ethanol will form when it traveles through the mass spectromoeter.

Answer 3

In mass spectrometry the molecular ion is the molocule of the sample that has been ionised but has not broken up during its flight through the instrument.
If you are asked for a species or anything to do with what has actually travled through the instrument you MUST GIVE THE FORMULA OF AN ION.
For ethanol C2H5OH+ or structural will be {CH3CH2OH+}.
Definition: Molecular ion is the molocule with one electron knocked off, (it is both an ion and a free radical.)
In general:
Molecular ion formed: M → [M]+.+ e

Question 4

What is detected when organic molocules are passed through a mass spectrometer.

Answer 4

When organic molecules are passed through a mass spectrometer, it detects both the whole molecule and fragments of the molecule.

Question 5

Why in general would reflux conditions be used. (heating under reflux)

Answer 5

This would ensure that a reaction will go to completion. For example fully oxidised.

Question 6

In the mass spectrometer which of the two parts of a fragment will be detected.

Answer 6

The fragment Ion [X+] will be detected wheres the corrasponding free radial will not be.

Question 7

What needs to be known when you are testing organic compounds.

Answer 7

You need to establish the functional group that is present.

Question 8

What does a solid compound suggest.

Answer 8

This suggests that there is a long carbon chain or possible ionic bonding for a hgher melting point. Note ionic bonding is much stronger than H- bonding that would be present in luiqids.

Question 9

What does a luiqid suggest about the nature of a compound.

Answer 9

It suggests that there is a medium length carbon chain or possibly hydrogen bonding or polarity present.

Question 10

What does a gaseous compoud tell you about its nature.

Answer 10

It tells you that it has a short carbon chain or little to no polarity.

Question 11

What does it suggest if a compound does disolve in water.

Answer 11

This suggests that there is polar groups if it does disolve in water or that there isnt polar groups if it doesnt disolve in water.

Question 12

What does it suggest if a compound is acidic.

Answer 12

This suggests that the compound is a carboxylic acid.

Question 13

Give the test tube reaction for an alkene functional group and the result if the test is possitive.

Answer 13

Shake with bromine water. The orange colour of the bromine will disapeare as (electrophilic addition occurs)

Question 14

Give the test tube test for the reaction of an alcohol functional group, R-OH. Give the observation if the test is possitive.
What specific alcoholes does this work for and one other functional group.

Answer 14

Add acidified K2Cr2O7 . The orange colour will turn will turn green (think same starting colour as with bromine) , and this will be the case for both primary and seconadry alcoholes in addition to aldehydes.

Question 15

Give a simple chemical test for an aldehyde functional group , R-CHO. State the observation if the test is possitive.

Answer 15

Warm with fehlings solution for colour change from blue to brick red precipitate.
Or use Tollens solution to get a silver mirror form.

Question 16

Give a simple chemical test for a carboxylic acid functional group, R-COOH. Give the observation if the test is possitive.

Answer 16

Add aqeous NaHCO3 to see effervescence of carbon dioxide evolved.

Question 17

Give a simple test to identify a holoalkane, R-X, and then also the test that would be done to specifically identify a chloroalkane , R-Cl .

Answer 17

Add NaOH 
Acidify with HNO3 
Add AgNO3 and warm 
Precipitate of AgX will form. 
Warming with silver nitrate would cause the slow formation of a white precipitate of AgCl.

Question 18

What can high resolution mass spactrometry be used for and why would it be needed to be done. Refer to how high resolution mass spectrometry is any different to normal spectrometry in your answer.

Answer 18

High resolution mass spectrometry can be used to determine the molecular formula of a compound from the accurate mass of the molecular ion.
High resolution mass spectroscopy can measure the mass to 5d.p. This can help differentiate between compounds that appear to have similar Mr (to the nearest whole number).
Forexample, the following molecular formulas all have a rough Mr of 60, but a more precise Mr can give the molecular formula. e.g
.Mr=60.02112 molecularformula=C2H4O2
Mr=60.05751 molecular formula=C3H8O
Mr=60.03235 molecular formula=CH4N2O

Question 19

A compound is found to have an accurate relative formula mass of 46.0417. It is thought to be either CH3CH2OH or H2NCH2NH2. Calculate the Mr of each compound to 4 decimal places to work out which one it is.
Given Accurate masses of atoms:
H = 1.0078 C = 12.0000 O = 15.9949 N = 14.0031

Answer 19

Working and answer: CH3CH2OH = (12.0000 x 2) + (15.9949 x 1) + (1.0078 x6) = 46.0417
H2NCH2NH2. = (12.0000 x 1) + (14.0031 x 2) + (1.0078 x6) = 46.0530
So it is CH3CH2OH

Question 20

What is the mass number of carbon.

Answer 20

Carbon has a value of 12.0000, as it is by definintion the standard reference.

Question 21

Give the two isotopes that chlorine and bromine can exist as and state the relative abundances of each.

Answer 21

Chlorine exists as Cl-35 (75%) and Cl-37(25%).

Bromine exists as Br-79( 50%) and Br-81 (50%).

Question 22

If an organic compound contains either chlorine or bromine then what can you expect the mass spectrum for that organic compund to look like. Also refer to the name of the concept you are refering to in your answer.

Answer 22

If a compound contains a chlorine or a bromine atom then two molecular ion peaks will occur : an M peak and an M+2 peak will occur due tothe two naturally occurring isotopes of chlorine or bromine.
This concent is the M / M+2 idea.

Question 23

Why can organic compounds containing both Cl and Br have their peaks considered in the same M and M+2 way even though the peaks will be in different ratios.

Answer 23

This is as both have two naturally occuring isomers with the same mass difference of 2. Cl-35 (75%) and Cl-37(25%). Br-79( 50%) and Br-81 (50%). Therefore even though the ratio of the peaks will differ due tothe difference in abundances the difference in mass will be the same between a compound containing one particular isomer and one that contains the other weather its Cl or Br.

Question 24

Give the M/Z value of the molecular ion peak for CH3Cl in a mass specrum and state the ratio that the peaks will be in.

Answer 24

CH3Cl will have a m/z value of M of 50 CH3Cl 35 and M+2 of 52 CH3Cl 37 The ratio of heights M:M+2 will be 3:1.

Question 25

Give the M/Z value of the molecular ion peak for CH3Br in a mass specrum and state the ratio that the peaks will be in.

Answer 25

CH3Br will have m/z value of M of 94 CH3Br79 and M+2 of 96CH3Br81 The ratio of heights M:M+2 will be 1:1 .

Question 26

Describe the four stages of what happens in an infra-red

spectrometer.

Answer 26

• Beam of infrared radiation containing a spread of frequencies is passed through a sample.
• The emerging radiation is missing the frequencies that correspond to the types of bond in the sample.

Question 27

Give the M/Z value of C2H3Cl3 (molecular Ion) and state the ratio that its peaks would be seen in on its mass spectrum.

Answer 27

h

Question 28

Outline the method that you would use to find the ratio of peaks for either a molecular ion or just an ion given , considering the naturally occuring isotopes in your answer.

Answer 28

NEED Doing

Question 29

Describe the four stages of what happens in an infra-red

spectrometer. Referer to the units plotted on the graph in your answer.

Answer 29

• Beam of infrared radiation containing a spread of frequencies is passed through a sample.
• The emerging radiation is missing the frequencies that correspond to the types of bond in the sample.
• The instrument will plot a graph of the wavenumber (proportional to frequency) against the intensity of radiation on the y axis ( also known as transmittance) there will be a dip in the intensity at the wavenumber (frequency) of a given bnd to show the radiation at this wavenumber has been absorbed.

Schematic diagram: Sourcse of IR ———–>smaple —>(less) detector/ instrument.

Question 30

Descrie the types of radiation that chemical bonds can absorb.

Answer 30

Can also absorb infra red radiation at characteristic frequencies , specific to that bond.

Question 31

What is another word for the intensity of radiation Emerging from a smaple and whch axis is this on and name the other variable it is plotted against. (In IR spectroscopy).

Answer 31

This is also known as transmittance and the transmittance (strength of emerging radiation ) is on the y axis. The wavenumber is the other variable and this is on the x axis.

Question 32

Give the two regions of the infra red spectrum and explain the purpose of each.

Answer 32

Above 1500 cm-1 – “Functional group identification”.
Below 1500 cm-1 – “Fingerprinting”
Below 1500cm-1 is a unique for every molecule. It is complex and contains lots of signals so picking out functional group signals is difficult. Where whole molecule vibrates.
Do not look below 1500 to identify functional groups apart from C-O in alcohols and esters.
A computer will compare the IR spectra against a database of known pure compounds to identify the compound. An exact match where the fingerprint region exactly superimposes on the fingerprint region in the data base confirms identity.

Question 33

Give the M/Z ion peaks for C2H4Cl2. State and explain the ratio that the peaks you have given will be in.

Answer 33

b

Question 34

Give the M/Z ion peaks for C2H4CBr2. State and explain the ratio that the peaks you have given will be in.

Answer 34

hj

Question 35

Give the M/Z ion peaks for C2H3Cl3. State and explain the ratio that the peaks you have given will be in.

Answer 35

g

Question 36

Give the M/Z ion peaks for C2H3Cl3. State and explain the ratio that the peaks you have given will be in.

Answer 36

n

Question 37

Give and explain a real life application to the absorption infra red radiation by bonds in infra red spectroscopy.

Answer 37

The absorption of infra-red radiation by bonds in this type of spectroscopy is the same absorption that bonds in CO2, methane and water vapour in the atmosphere do - that causes the green house effect.UV wavelength radiation passes through the atmosphere to the Earth’s surface and heats up Earth’s surface. The Earth radiates out infrared long wavelength radiation.
The C=O Bonds in CO2 absorb infrared radiation so the IR radiation does not escape from the atmosphere.
This energy is transferred to other molecules in the atmosphere by collisions so the atmosphere is warmed.

Question 38

When would the fingerprint regionally be used.

Answer 38

When organic molocules have identical bonds.

Question 39

Impurities and also more specifically what the fingerprint region is , finish wierd chlorine questions.

Answer 39

n