6.3 Analysis

Question 1

what TMS is used for

Answer 1

reference peak for proton NMR spectra

Question 2

TMS stands for

Answer 2

tetramethylsilane

(CH3)4Si

Question 3

solvents for proton NMR

Answer 3

sample needs to be in solution
solution must not have any C or H
deuterated solvents used (e.g. CDCl3, D2O)

Question 4

D2O shake in proton NMR

Answer 4

shake sample with D2O
replaces hydrogen atoms on sample with deuterium
peaks on any functional group containing hydrogen will disappear

Question 5

chemical shift in proton NMR

Answer 5

protons attached to electronegative atoms will be shifted more downfield (higher PPM)
protons in same environment will have the same chemical shift

Question 6

spin-spin coupling in proton NMR

Answer 6

high resolution gives more complex signals (doublets, triplets etc)
splitting pattern depends on number of hydrogen atoms on adjacent atoms

Question 7

splitting pattern formula

Answer 7

number of peaks = number of chemically different H’s on adjacent atoms + 1

ratio of height: draw peaks with heights such as Fibonacci triangle

Question 8

what integration shows in proton NMR

Answer 8

number of hydrogens at that environment / peak

Question 9

how coupling occurs

Answer 9

isotopes of the same atom influence each other

Question 10

why only singlets in carbon NMR

Answer 10

likelihood of C-13 being next to each other in one molecule very rare

Question 11

solvent definition

Answer 11

liquid used to dissolve things

Question 12

solute definition

Answer 12

substance that dissolves in a solvent to make a solution

Question 13

adsorption definition

Answer 13

when particles adhere to the surface of a solid

Question 14

partition definition

Answer 14

distribution of 2 solutes between 2 phases in a separation process

Question 15

mobile phase definition

Answer 15

phase which moves through the stationary phase (liquid or gas)

Question 16

stationary phase definition

Answer 16

phase that doesn’t move

may be a solid (TLC) or liquid (GC) held by solid support

Question 17

TLC chromatography phases

Answer 17

mobile phase: organic solvent

stationary phase: solid (aluminium oxide or silicon oxide-coated plastic)

Question 18

thin layer chromatography method

Answer 18

place sample using micro pipette on TLC plate (base line)
place ~1cm^3 depth solvent in beaker
add TLC plate to beaker
add lid to prevent solvent evaporation
leave for mobile phase to reach almost the top
take out TLC and leave to dry (mark where solvent got to)
view results (e.g. with UC, ninhydrin, iodine crystals)

Question 19

gas chromatography phases

Answer 19

mobile: gas e.g. Ne, Ar, N2
stationary: liquid or solid on a solid support

Question 20

how gas chromatography works

Answer 20

separation occurs by relative solubility into liquid or adsorption onto solid
retention times measured (longer = less soluble)

Question 21

limitation of gas chromatography

Answer 21

similar compounds have similar retention times (peaks may hide each other)
hard to identify unknown compounds as retention times depend on flow rate of carrier gas and temperature of column

Question 22

GC-MS uses irl

Answer 22

analysis in forensics
environmental analysis
airport security
space probes

Question 23

interpretation of gas chromatogram

Answer 23

peak integrations (area under each peak) can help determine concentration of each component
retention times used to identify components by comparing to known components

Question 24

finding concentration of components method (external calibration)

Answer 24

prepare standard solutions of known concentrations of compound being investigated
obtain gas chromatograms for each standard solution
plot calibration curve of peak area against concentration
obtain gas chromatogram of compound being investigated under same conditions
use calibration curve to measure concentration of compound

Question 25

nuclear spin for NMR spectroscopy

Answer 25

only detects isotopes with an odd number of nucleons (e.g. 1H or 13C)

Question 26

region of EM spectrum used for spectroscopy

Answer 26

radio waves

Question 27

uses of NMR spectroscopy in medicine

Answer 27

MRI scanning
providing diagnostic information
body scanning

Question 28

melting point determination helps how

Answer 28

determines melting point of substance which:
• helps determine final product (compare to table of known melting points)
• determine purity of product (100% = sharp, range of melting points = not pure)