6.3

Question 1

what’s the stationary phase in tlc
examples?

Answer 1

the solid material the liquid moves up
inert material covered in an absorbent chemical eg glass with aluminium oxide

Question 2

what’s the stationary phase in gas chromatography
examples?

Answer 2

the solid or liquid coating on a coiled tube eg hydrocarbon with high boiling point

Question 3

what’s the mobile phase in tlc

Answer 3

moves in a definite direction
liquid solvent
eh organic solvent

Question 4

what is the stationary phase (general)

Answer 4

the phase that is fixed in place

Question 5

what is the mobile phase (general)

Answer 5

phase that moves in a definite direction

Question 6

what is the Rf value

Answer 6

a comparison between how far a component has moved compared to the solvent in thin layer chromatography

Question 7

what is retention time

Answer 7

the time taken for a component to travel from the inlet to the detector in a gas chromatograph

Question 8

how do results look in gas chromatography

Answer 8

chart of absorption against time, the area under the absorption peaks is proport

Question 9

how do you test for alkenes (unsaturation)

Answer 9

add bromine water + shake well, should decolourise

Question 10

how do you test for haloalkanes

Answer 10

dissolve and add dilute nitric acid and silver nitrate
creates silver halide precipitate:
- chloride white
- bromide cream
- iodide yellow

Question 11

how do you test for a carbonyl

Answer 11

add 2,4-DNPH yellow orange red precipitate forms

Question 12

how do you test for an aldehyde

Answer 12

add tollens reagent a silver mirror will form

Question 13

how do you test for aliphatic carboxylic acids

Answer 13

ph of a weak acid, will effervesce when reacting with reactive metals or metal carbonates

Question 14

how do you test for phenols

Answer 14

ph of weak acid
won’t react with the carbonate ion (no effervescence)

Question 15

how do you test for alcohols

Answer 15

acidified potassium dichromate goes green and next product can be tested to check if primary or secondary (no observation for tertiary)

Question 16

brief explanation of nmr

Answer 16

1H and 13C have spin. compounds with these isotopes are out in a large magnetic field (direction of spin matches mag field direction). energy in the form of radio waves force the spins to change direction, energy required to change the alignment indicates the environment

Question 17

what chemical is used as a reference
why (internal standard)

Answer 17

TMS
(CH3)4Si
has lots of Cs and Hs in the same environment (strong peak at 0ppm)
symmetrical and non polar
nontoxic, inert, doesn’t disrupt signals, low boiling point so can be distilled off at the end

Question 18

what kind of solvents do you need to dissolve the sample for nmr testing
why

Answer 18

deuterated solvents
contain D (2H) instead of H (1H), D doesn’t have spin, so won’t show on the spectrum and disrupt the spectrum

Question 19

what solvent is commonly used in nmr

Answer 19

CDCl3

Question 20

how to approach carbon nmr questions (table)

Answer 20

columns: carbon(show what it’s bonded to and underline carbon we’re talking about)
functional group (what’s shown on the data sheet)
chemical shift (ppm)

Question 21

what is chemical shift

Answer 21

the scale that compares the frequency of NMR absorption with the frequency of the reference peak of TMS

Question 22

what are equivalent protons

Answer 22

hydrogen atoms bonded to the same atoms that therefore experience the same magnetic field in the NMR spectrometer

Question 23

difference between low and high resolution proton NMR

Answer 23

low res has one peak per environmentally different group protons
high res can have multiple peaks representing one environment, depending on the splitting pattern

Question 24

what is considered in splitting patterns

Answer 24

the effect of adjacent chemically different protons on another signal in a given environment

Question 25

why do splitting patterns exist

Answer 25

the spin of the proton producing the signal is affected by each chemically different adjacent protons

Question 26

how to figure out splitting pattern

Answer 26

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

Question 27

why are OH and NH groups hard to identify in nmr

Answer 27

peaks can appear across a wide range signals often broad usually no splitting pattern

Question 29

how is D2O used in nmr

Answer 29

proton nmr spectrum run add D2O to sample and shake second proton nmr spectrum run OH and NH proton peaks disappear

Question 30

why do you need to shake D2O

Answer 30

CDCl3 and D2O are immiscible

Question 31

why does the D2O shake work

Answer 31

because the deuterium in D2O exchanges with the H present in OH and NH

Question 32

what is special about multiplicity with OH and NH why

Answer 32

they only show one peak (always a singlet) and don’t affect the signal splitting of adjacent protons because the H on the OH and NH rapidly exchanges with protons on other molecules (not attached to a particular O or N long enough to register a splitting signal)

Question 33

how to use computer integration to find the ratio of protons in each environment

Answer 33

measure distance between the flat lines before and after peaks of environment put in ratio

Question 34

how to answer proton nmr questions (table)

Answer 34

chem shift chem env H in env chemically different adjacent H’s splitting pattern