LABORATORY TOPICS

Question 1

Define an Enantiomer.

Answer 1

non superimposable mirror images. have opposite configurations (R)/(S) at all stereo centres.

Question 2

What is “achiral” ?

Answer 2

means there is an internal mirror plane of symmetry. Meso compounds are achiral. (superimposable on their mirror image).

Question 3

Define a Diastereomer.

Answer 3

different configurations at some, but not all, the chiral centres.

Question 4

E/Z refer to priority groups and trans/cis refer to longest chain. [true or false]

Answer 4

TRUE.

Question 5

What is distillation? What is it used for?

Answer 5

Separation process, used to purify liquids. transfers vapour to a different apparatus and condenses.

Question 6

Difference between fractional and simple distillation.

Answer 6

fractional is used for liquids with similar boiling points. simple is used for liquids with different boiling points.

Question 7

What does the temperature change represent on a Liquid-Vapour Diagram?

Answer 7

Once you’ve finished distilling the first liquid at TempA, the temp will change to begin boiling the more volatile liquid.

Question 8

Why use a Reflux apparatus?

Answer 8

allows a reaction to take place at a HIGH constant temperature (boiling point of the solvent) without loose due to evaporation.

Question 9

In TLC analysis, how can you compare polarity?

Answer 9

If the plate is silica (polar), the less polar compounds will move further up the plate as there’s less “interactions” with the plate. Rf value is another way. Lower Rf values means more polar molecule.

Question 10

How can you move the dots further up the plate?

Answer 10

Make the solvent more polar.

Question 11

Name 3 main Reductive Processes.

Answer 11

1. Catalytic Hydrogenation (adding H2)
2. Hydride Reduction (adding hydride, then H)
3. Dissolving Metal Reduction (adding e- then p+)

Question 12

What acts as the Nucleophile in Hydride Reduction?

Answer 12

the hydride H- (sourced from reagents LiAlH4 or NaBH4) and reduces the carbonyl.

Question 13

What functional groups can NaBH4 reduce?

Answer 13

can not reduce carboxylic acids, esters or ethers. Only ketones and aldehydes.

Question 14

Describe the effect of the Grignard Reagent.

Answer 14

The magnesium creates a partially bonded carbanion. This makes the R group of R–MgX act as a good nucleophile. The reagent adds to the electrophilic carbonyl group !!

Question 15

The grignard reagent acts as an electrophile and is basic. [true or false]

Answer 15

False. The reagent is NUceleophilic and Basic.

Question 16

In aldol addition, what is the nucleophile and what is the electrophile?

Answer 16

Enolates act as a good Nu and Carbonyl C acts as electrophile.

Question 17

Explain briefly the aldol addition.

Answer 17

An enole/enolate from an aldehyde/ketone reacts with another aldehyde/ketone forming a new C-C bond. After this, they often go through dehydration.

Question 18

What is required for the aldol addition to occur?

Answer 18

there must be an alpha-hydrogen in the structure. (i.e., adjacent to the C=O). as well as a base catalyst to deprotonate said hydrogen.

Question 19

Which are more reactive to Nucleophiles, aldehydes or ketone?

Answer 19

aldehydes. consider resonance and hyper conjugation.

Question 20

Explain a conjugated alkene.

Answer 20

2 double bounds connected by a single bond, share delocalized electrons, overlapping p-orbitals. trans orientation is more table than cis.

Question 21

When dehydrating alcohol’s, what product is most favoured? (consider diene product)

Answer 21

The conjugated formation is the most favoured product, in Diels-Alder reaction

Question 22

explain Schiff’s Reagent

Answer 22

to test for aldehydes. positive when magenta colour appears.

Question 23

explain Tollen’s Test

Answer 23

to test for aldehydes. positive when silver/metallic colour appears. redox reaction occurs.

Question 24

explain Iodoform Test

Answer 24

to test for methyl ketones. positive when pale yellow solid crystals form.

Question 25

explain Ferric Chloride Test

Answer 25

to test for phenols. negative when pale yellow colour, positive when dark purple.

Question 26

explain 2,4-DNP

Answer 26

used to test for aldehydes + ketones on aromatic ring. does NOT react with amines, esters or carboxylic acids. positive test means conjugated double bond to aromatic. orange-red derivatives.