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chemistry > Organic Synthesis And Analysis > Flashcards

Organic Synthesis And Analysis Flashcards

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1
Q

What compound is used as a reference for NMR (draw it)

A

Tetramethylsilane

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2
Q

Why is TMS used as a reference (3)

A

It produces a single intense peak (all hydrogen and carbon atoms are equivalent)

It is non toxic and chemically inert

It is upfield (to the right) from nearly all peaks produced by hydrogen/ carbon atoms

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3
Q

What is 13C nmr used for

A

To determine the number of carbon atoms in different environments

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4
Q

What is the relationship of chemical shift values and the position of carbon atoms

A

The closer a c atom is to an electronegative atom the higher its chemical shift value

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5
Q

What is the integration ratio

A

The area under the peaks on a 1H nmr spectrum are proportional to the number of hydrogen atoms in a specific environment

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6
Q

What is the n+1 rule

A

The number of peaks in one cluster is one more than the number of hydrogens attached to the neighbouring carbon

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7
Q

What is the name of something with 1,2,3 or 4 peaks

A

Singlet

Doublet

Triplet

Quartet

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8
Q

What is the pattern of integration ratios

A

Binomial expansion

(1+x)^n where n us number of neighbouring hydrogens

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9
Q

What does an integration of 3 or 9 usually represent

A

2 or 3 methyl groups in same environment

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10
Q

What is the ruling in symmetrical molecules

A

Equivalent hydrogen atoms have no effect on each other so there is no splitting

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11
Q

What solvents are used for 1H nmr

A

CCl4

CDCl3

CD2Cl2

D2O

Deterioum is used instead of hydrogen so that the hydrogen in sample isn’t confused with the one in the solvent

Refer to photo

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12
Q

What is chromatography

A

A series of analytical techniques used to separate mixtures of compounds

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13
Q

What is the stationary phase (3)

A

Phase that doesn’t move
It can be solid or liquid

The compounds in mixture adsorb to it

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14
Q

What is the mobile phase

A

The phase that moves

Based on solubility the compounds move faster

Can be liquid or gas

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15
Q

What is RF in TLC

A

Distance travelled by spot / distance travelled by solvent front

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16
Q

What is true for rf values

A

Always less than 1

17
Q

What is the stationary phase in tlc

A

A piece of plastic coated with a thin layer of a solid like silica it alumina

18
Q

What is the mobile phase in TlC

A

A liquid solvent that moves up the plate

19
Q

Why is the line drawn in pencil

A

Ink is mixture of different inks that will also undergo tlc

Pencil is insoluble

20
Q

Why are the spots not close together

A

If they are too close they merge as they travel up the plate

21
Q

Why is the solvent below the pencil line

A

So that the sample doesn’t dissolve in the solvent before it can travel up the plate

22
Q

Why must you only use small spots

A

If it’s too big there will be too much sample so it can’t be carried by the solvent which leads to elongated smudges not clear tlc spots

23
Q

Why is the plate removed before the solvent reaches the top

A

For a clear reference of solvent front to calculate the rf values

24
Q

Why must the chamber have a lid

A

To have a saturated atmosphere of solvent so the plate doesn’t dry out

25
Q

What is the procedure of column chromatography

A

A glass tube is filled with the stationary phase (alumina or silica powder to increase surface area ) or an ion exchange resin in form of small granules

A filter or plug is used to retail the solid in the tube

Solvent is added to give or all the powder

26
Q

What is the stationary phase in column chromatography

A

Silica or alumina gel

27
Q

What is the mobile phase in column chromatography

A

A liquid solvent (eluent)

28
Q

What is the relation between retention times and solubility in column chromatography

A

The greater the solubility in the mobile phase the shorter its retention time and the faster it will come out of the column

29
Q

How do you determine whether your solvent should be polar or non polar

A

A polar sample has greater solubility in a polar solvent

A non polar sample has greater solubility in a non polar solvent

30
Q

What happens in gas chromatography

A

A column is paced with a solid or solid coated by a liquid and a gas is passed through the column under pressure at high temperature

31
Q

What is the stationary phase in gas chromatography

A

A capillary glass or metal tube filled with a solid or a liquid adsorbed onto the solid (this is the column)

32
Q

What is the mobile phase in gas chromatography

A

An inert carrier has such as helium, argon or nitrogen used to separate the volatile components of a mixture

33
Q

How is retention then recorded in gas chromatography

A

At the end of the column a range of detectors identify each components for example mass spectrometry

34
Q

What is gas chromatography mass spectrometry commonly used in (3)

A

Forensics

Environmental monitoring

Airport security system

35
Q

Why is mass spectrometry used

A

It is sensitive enough to detect minute quantities of substances

Produced spectra which can be compared to spectra of known compounds

36
Q

What is retention time based on

A

Difference in balance between solubility in the mobile phase and adsorption to the stationary phase

chemistry (23 decks)

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