organic synthesis nmr chromotography

Question 1

how do chemists make drugs that are cost effective safe and enviromentally freidnly?

Answer 1

1) using starting products that have low toxicity
2) using few steps to maximise atom economy and yield
3) To use minimum solvents as they are toxic and produce waste

Question 2

what are the 2 types of nmr

Answer 2

hydrogen1 nmr

carbon13 nmr

Question 3

what do nmr machines detect?

Answer 3

if an atom has an odd number of nucleons (protons + neutrons) it produces nuclear spin
this creates a weak magnetic field
nmr detects how these fields are affected by a larger external field

Question 4

what is tetramethylsilane used as and why

Answer 4

standard when looking at chemical shift

it is inert and non toxic

Question 5

how do you work out carbon environment for cyclic compounds?

Answer 5

work out symmertry line of environment

Question 6

what is an intergration trace

Answer 6

when it is difficult to work out the area of hydrogen nmr

a height ratio can correspond to the area ratio

Question 7

what solvent is used for hydrogen nmr

Answer 7

we cant used hydrogen based solvents (H2O) as the peaks would show in the sprectrum
Instead you can use

CDCL3/CCL4

Question 8

why is Tetramethylsilane used?

Answer 8

non toxic
inert
easily removed
single strong peak
volatile

Question 9

what are the two stages of chromotography?

Answer 9

mobile-

stationary-sillica allmunia

Question 10

what are the steps of chromotography

Answer 10

mark the base line with a pencil
add drops of mixture along base line
dip into solvent making sure it is slighlty beneath base line
allow solvent to move up and to near the top
take paper out of solvent and mark solvent front

Question 11

how does chromotography worK?

Answer 11

drops dissolve in the solvent

some chemicals in drops may not dissolve and stick to the stationary phase

Question 12

what to do if the spots are colourless on the chromotography?

Answer 12

use fluorescent dye and UV light to stain the whole sheet the dots can then be traced around
leave the sheet inside a jar with iodine crystals these then sublime and the dots are stained purple

Question 13

what are RF values fixed for?

Answer 13

temperature
solvent
TLC plate make up

Question 14

what is column chromotography?

Answer 14

used to seperate larger mixtures

Question 15

how does column chromatogrophy work?

Answer 15

A burrete is packed with silica/ alumnia this acts as a stationary phase
the mixture and solvent are run through
the solvent is run through continously
the different compounds in the mixture run through at different times seperating them

Question 16

what is gas chromotogreaphy used for?

Answer 16

seperate liquids that are volatile

Question 17

how does gas chromatography work?

Answer 17

thin column wind up inside an oven , coated with a solid/viscous liquid(oil) thats acts as stationary phase
the sample in injected and carried by an inert gas (nitrogen) mobile phase
different samples take different times to travel across to detector (retention time)

Question 18

Explain why different amino acids have different Rf values

Answer 18

Amino acids have different polarities

Therefore, have different retention on the stationary phase or different
solubility in the developing solvent

Question 19

Outline briefly why chromatography is able to separate a mixture of compounds.
Practical details are not required.

Answer 19

stationary phase made from sillica/alumnia

mobile phase