organic compound analysis

Question 1

spectroscopic techniques, region of spectrum & type of energy level transition

Answer 1

NMR - radio waves - nuclear spin states. makes nucleus flip in an applied magnetic field
IR - infrared - vibrations of bonds - twists, bend, stretch
colorimetry, UV-visible, AAS - visible & ultraviolet - valence e- in molecules and atoms move to higher energy levels.

Question 2

principals of spectroscopy

Answer 2

• Atoms and molecules absorb and emit electromagnetic radiation of specific energies
• Atoms and molecules undergo a change when they absorb electromagnetic radiation
• Different parts of the electromagnetic spectrum affect atoms or molecules in different ways.
• This allows different spectroscopic methods to identify different parts of molecules and hence the identity of those molecules

Question 3

IR features

Answer 3

expensive, IR region, fast once sample prepared, gases, liquid & solids, absorption, plot of transmittance against wavenumber

Question 4

mass spectrometry features

Answer 4

identify molar mass by using m/z

can distinguish between isomers

Question 5

m/z

Answer 5

mass to charge ratio (mass of a cation divide by its charge)

Question 6

Fragmentation

Answer 6

the dissociation of unstable molecular ions
occurs by breaking almost any bond in molecular cation
M+ -> X+ + R. (radical, .rep unpaired e-)

Question 7

Base peak

Answer 7

peak formed from ion fragment with the greatest relative intensity

Question 8

Molecular ion peak

Answer 8

peak formed from the ionised un-fragmented form of a molecule

Question 9

Isotopes

Answer 9

two or more forms of the same element that have the same number of protons but different numbers of neutrons

Question 10

common fragments and m/z

Answer 10

CH3+ =15
OH+ =17
CH3CH2+, COH+, CHO+ =29
CH3O+ = 31
35Cl, 37Cl = 35,37
COOH+ =45
79Br, 81Br =79,81

Question 11

NMR ft

Answer 11

radio waves region = different compounds reacts with radio waves in different ways - affect the nucleus
absorbance spectroscopy
proton H1 NMR & C13 NMR
fast, expensive, hazardous(strong magnetic field)
qualitative only

Question 12

H or C environment

Answer 12

dictates by what its attached to eg atoms, atom groups

Question 13

splitting (high res H NMR)

Answer 13

peaks which involve hydrogen on neighbouring carbon atom split according to the n+1 rule where n is number of hydrogen atoms on neighbouring carbon atom/s

Question 14

Chromatography

Answer 14

analytical technique used to determine the identity of components in a mixture as well as their concentration

Question 15

Stationary phase

Answer 15

solid onto which the components of a sample adsorb

Question 16

Mobile phase

Answer 16

phase that flows through the stationary phase carrying components of a sample with it

Question 17

Adsorption

Answer 17

component adheres to the stationary phase (in the context of chromatography)

Question 18

Desorption

Answer 18

a component is released from the stationary phase and dissolves into the
mobile phase (in the context of chromatography)

Question 19

HPLC

Answer 19

(High performance liquid chromatography) type of chromatography technique which pumps the mobile phase through a very tightly packed stationary phase under high pressure

Question 20

calibration curve

Answer 20

curve that is developed from a set of known standards and is used to identify the concentration of a sample

Question 21

Retention time, Rt

Answer 21

measure of time taken for a component to travel through a chromatography column e.g. HPLC column
longer is adsorb more strongly to SP or bigger molecules

Question 22

Eluent

Answer 22

combination of the mobile phase and sample that moves through the HPLC column

Question 23

effect of stronger adsorption on retention time

Answer 23

increases

Question 24

polarity of molecules and attraction to SP and MP

Answer 24

polar molecules attracted to polar stationary phase/mp

non polar molecules attracted to non polar stationary phase/mp

Question 25

hplc analysis, sp, mp and measurement

Answer 25

analysis - large organic compounds and molecules, not volatile small compounds
sp - fine waxy solids, surface area = better separation
mp - pure or mixture solvent. high pressure = densely packaged.
measurement - retention time (qual) and peak area for conc (quant)

Question 26

factors affecting Rt

Answer 26

• identity and composition of SP
• identity and composition of MP
• length of column
• MP flow rate
• surface area of the SP

Question 27

primary standards qualities

Answer 27

obtainable in pure form
known chemical formula
easy to store without deteriorating or reacting with the atmosphere
high molar mass to minimise effect of errors in weighing
inexpensive
highly soluble in water

Question 28

how to create a standard solution

Answer 28

• Mass of primary standard is weighed
• Primary standard is transferred to volumetric flask
• Deionised water is added to the volumetric flask until primary standard is dissolved
• Solution is left at rest to allow any volume expansion from newly-formed intermolecular bond
• Deionised water is added until the meniscus lies on the required volume

Question 29

equivalence point

Answer 29

solutions have reacted in exact mole ratio shown by reaction equation/the point in the reaction where neither reactant is in excess

Question 30

end point

Answer 30

point where indicator changes colour

Question 31

rinsing glassware

Answer 31

burette & pipette = acid/base to be transferred by them

volumetric flask & conical flask = deionised water

Question 32

ph curves

Answer 32

sa,sb = equivalence point 7
sa,wb = equivalence point less than 7
wa,sb = equivalence point greater than 7

Question 33

effect of rinsing burette with water (unknown in titration flask)

Answer 33

overestimation - burette solution diluted so more is used

underestimation if unknown is in burette

Question 34

effect of rinsing pipette with water (unknown in titration flask)

Answer 34

underestimation - aliquot solution in titration flask is diluted (overestimation if unknown is in burette

Question 35

effect of indicator chosen turns colour too soon (unknown in titration flask)

Answer 35

underestimation (overestimation if unknown is in burette)

Question 36

effect of water in titration flask

Answer 36

no effect

Question 37

effect of concentration of standard is lower than calculated

Answer 37

overestimated - fewer moles of standard than expected, substance analysed will appear to have higher conc

Question 38

effect of concentration of standard is higher than calculated

Answer 38

Underestimation - more moles of standard than expected, substance analysed will appear to have lower conc