organic analysis

Question 1

what does NMR give information about

Answer 1

position of the 13C or 1H atoms in a molecule that resonates the different frequencies

Question 2

what does the number of peak in 13C NMR represent

Answer 2

the number of carbon environments in a molecule

Question 3

what does the numbers of peaks in 1H nmr spectra represent

Answer 3

each peak in a 1h nor spectra has an integration trace which chooses the relative number of 1h in each environment

Question 4

what does high resolution 1h have the ability to show

Answer 4

spin-spin coupling, this is useful because spin spin coupling causes splitting pattens which give information about neighbouring hydrogen atoms, the splitting pattern is determined by N+1 rule

Question 5

what is n+1 rule

Answer 5

if there are no hydrogen atom attached to the carbon atoms adjacent to a 1H environment, the the peak reprinting that environment will be spilt into n+1 peaks

Question 6

what is chemical shift

Answer 6

it depends on the molecular environment, it relates to the difference in frequency between a chemical environment and TMS

Question 7

what is integrated spectra

Answer 7

indicates the relative number of the 1H atom in different environments

Question 8

how is 1H Nmr spectra obtained

Answer 8

using samples disabled in deuterated solvents or CCL4

Question 9

what is tertramethylsaline

Answer 9

TMS as a standard used to measure an NMR spectrum peak against it, the 4 methyl groups are in the same chemical environment and produce an intense signal

Question 10

what is a denatured solvent

Answer 10

any H atoms are replaced with deuterium so have no overall effect of the spectra

Question 11

what is chromatography used for

Answer 11

used to spectate and identify the components in a mixture

Question 12

what is the mobile phase

Answer 12

substance in chromatography that carries the soluble components of the mixture

Question 13

what is the stationary phase

Answer 13

substance in chromatography that holds back components that are attracted to oy

Question 14

how are components separated

Answer 14

each components in the mixture has a different level of solubility in the mobile phase and retention in the stationary phase

Question 15

what is thin layer chromatography

Answer 15

a plate is coated with a solid and a solvent moves up the plate column, an organic solvent is used as the mobile phase. A sheet coated with a thin layer of silica gel acts as the stationary phase. Thin layers can be used to separate and identify amino acids by their rf values.

Question 16

how are amino acids separated by thin layer chromatography

Answer 16

different amino acids have different r groups, so they have different affinities for the solvent therefore will move up the plate at different rates depending on their affinity

Question 17

why do we add a visible developing agent

Answer 17

amino acids are colourless

Question 18

what is column chromatography

Answer 18

a column is packed with a solid and a solvent moved down the column, silica is packed in a narrow column and cats as a stationary phase, the mixture if dissolved in a solvent and poured through the column this acts as a mobile phase

Question 19

what is gas chromatography

Answer 19

a column is packed with a solid or with a solid coated by a liquid and a gas is passed through the column under pressure at high temperature, the stationary phase is a solid or liquid coating inside a long coiled tube, an inert has e.g. N2 is produced.

Question 20

what is retention time

Answer 20

the time taken for a component to leave the coil is the retention time, this can be compared with standards to identify substances.

Question 21

what is a chromatograph

Answer 21

shows the retention times as a series of peaks with the are under each peak being proportional to the amount of components present

Question 22

what does separation depend on

Answer 22

the balance between solubility in the moving phase and retention by the stationary phase

Question 23

how to identify different substances

Answer 23

by the retention time and rf values

Question 24

what is mass spectrometry used for

Answer 24

analyse the components separated by gas chromatography, the mass spectrum of each component can be compared to spectra in a database, allowing components to be identified with greater certainty