10. Organics (SL+HL) Flashcards

Question

What are the two types of stereoisomerism?

Answer 1

- E/Z isomerism - optical isomerism

Answer 2

- Would have to break the C=C double bond to rotate around it -If both C of the C=C have two different groups attached, the molecule has E-Z isomers. -E= entgegan (highest priority opposite) -Z=zusammen (highest priority together)

Answer 3

Cahn-Ingold Priority (CIP) rules assigned priority of groups attached to C=C- the higher the atomic number of the group attached to the C's, the higher the priority (if they are the same, look at the atoms attached to those atoms)

Answer 4

Molecular have optical isomers if their mirror images are non-superimposable i.e. not the same.

Answer 5

Molecules containing a C with four different groups attached to it exhibit optical isomerism. A carbon atom that has four different groups attached is called a chiral(asymmetric) carbon atoms.

Answer 6

Two compounds that are optical isomers of each other are called enantiomers.

Answer 7

A mixture containing a 50/50 mixture of the two isomers(enantiomers) is described as being racemic mixture.

Answer 8

Optical isomers have the same chemical and physical properties as each other, except for their effect on plane polarised light(and how they react with other chiral compounds).

Answer 9

Light is a form of electromagnetic radiation and so consists of waves that vibrate in many directions perpendicular to the direction of travel. Some substances have the ability to remove from normal light all the light waves except those vibrating in a single plane - producing plane-polarised light.

Answer 10

Optical isomers can rotate the plane of polarised light (and so these compounds are said to optically active).

Answer 11

One enantiomer rotates it in one direction and the other enantiomer rotates it by the same amount in the opposite direction.

Answer 12

A racemic mixture will have no effect on the plane of the light - it is optically inactive ( each enantiomer cancels out the effect of the other).

Answer 13

1. Set up apparatus ( melting point apparatus, melting point tubes, thermometer) to perform a melting point determination as shown in the diagram below. [ Don't use wooden burette stand to hold melting point apparatus] 2. Take melting point tube & seal one end in Bunsen burner 3. Place few crystals of solid in tube (make sure that it goes right down to bottom of tube by gently tapping it on bench) 4. Attach melting point tube to thermometer so that sealed end of tube which contains crystals is next to bulb of thermometer & place it in melting point apparatus. 5. Warm boiling tube with a low flame, stirring oil constantly. Try to keep rate of warming down to around 10°C/min initially & 2°C/min near melting point of solid. 6. Watch crystals carefully & record temp at which they melt. If solid is solid pure ethanamide, it should melt over small temp range (81-82°C)

Answer 14

1. Set up apparatus to perform a boiling point determination as shown in diagram below 2. Place small quantity (around 2 cm^3) of ester in a boiling tube that is being held in a clamp & stand 3. Adjust height of thermometer so that bulb of thermometer is around 1 cm above level of liquid in boiling tube 4. Add couple of piece of porous pot to liquid & then heat it very gently with a low flame 5. When liquid is boiling gently, record temp of vapour

Answer 15

1. Set up apparatus to perform a distillation as shown in diagram below. Ask for help if you get stuck 2. Place 25cm^3 of impure ethyl ethanoate in medium sized round bottom flask & add a few pieces of porous pot to promote smooth & even boiling 3. Make sure that there is water running through condenser & then gently begin begin to heat flaks until liquid begins to boil. Once liquid begins to distil over,, adjust heat such that drops are coming over at around one second 4. Make a note of boiling point of ethyl ethanoate as it distils over. 5. When there is no more liquid left in original flask or boiling temp begins to rise, stop heating flask & allow apparatus to cool down 6. Take distillate in small round bottom flask & add a spatula of anhydrous magnesium sulphate. Carefully swirl flask to aid action of drying agent. Continue adding small quantities of magnesium sulphate until drying agent no longer clogs together on swirling. 7. Filter off drying agent, using a fluted filter paper, leaving pure ester (which should be a clear, colourless liquid) in a small conical flask. You do not need to do a further distillation on this liquid.

Answer 16

1. Set up apparatus to perform a reflux as shown in diagram below. Ask for help if you are not sure what to do. 2. Place 10cm^3 each of ethanol & ethanoic acid in round bottom flask together with around 1 cm^3 of conc. sulphuric acid. Shake flask carefully to ensure reactants are well mixed & then add a few pieces of porous pot to promote smooth & even boiling. 3. Make sure that there is water running through condenser & then gently begin to heat mixture using burner. Warmer mixture until it is boiling, then leave it to reflux for around 15 mins. During this time you should keep eye on apparatus to ensure that mixture is not boiling too vigorously & that vapour is being condensed effectively - level of vapour shouldn't get much above halfway up condenser before it is turned back into liquid. If it should go much higher there is a risk that it will come out of top of condenser & catch fire! 4. At end of 15 mins, remove heat & allow mixture to cool for a few mins. then pour reaction mixture into a250ml beaker containing around 50 cm^3 of sodium carbonate solution. Once any reaction has stopped, carefully smell mixture to detect if any ester has been formed - esters have sweet , fruity smell.

Answer 17

1. Weigh out accurately around 3.0g benzoic acid. Place in a 250ml beaker & add around 80cm^3 of distilled water. 2. Warm beaker & stir mixture until solid just dissolves - add more distilled water as necessary if solid does not dissolve. It's important not to add too much solvent otherwise crystals will not form on cooling. 3. Fold a fluted filter paper (ask to be shown how) & place it in a short-stemmed filter funnel sitting on a clean 100ml conical flask. Filter solution while hot, making sure you pour it carefully. Wash out any residues from beaker with a little hot distilled water. 4. Allow conical flask to cool slowly - If no crystals appear to be forming, stand flask in a beaker or saucepan of ice-water or scratch side of conical flask with a glass rod. 5. Filter off crystal using a Buchner funnel & flask. Wash out any residual crystals from flask using a little cold distilled water & then crystals in Buchner funnel also with some cold distilled water. 6. Remove crystals from funnel & spread them on a piece of dry filter paper gently compress them between pieces of filter paper to dry them. Break up any large lumps with a spatula. 7. When they are completely dry, weigh your yield & then determine melting point of crystals. (You can heat oil reasonably rapidly up to 100°C with vigorous stirring, then heat slowly). 8. Determine & record melting point of pure benzoic acid & calculate percentage yield.