organic chem error log

nucleophilic substitution addition

my mistake

• I drew the structure of the compound incorrectly — pay great attention to detail - after I write out every line or compound, ensure that I check it for stupid errors

• my chain of reasoning was incomplete - for my reasoning, I stated that the C=C bond creates no polarity

• however there’s an even bigger reason as to why that happens - the nucleophile and the electron density repel each other

shortcuts/what to do next time

• always ensure my chain of reasoning is complete

• check every line of working/drawing/explanation, after I write it out

xoxox

equation to show reduction of ketone

my mistake

• butanone had the incorrect structural formula (there was an additional H next to the carbon that was bonded to the O)

shortcuts

• Rmb the nucleophile is represented as [H] and there’s always 2H-

• reduction is gain of electrons — these can be gained through the H- ion

xoxoxo

racemic mixtures and polarised light

my mistake

• my chain of reasoning was incomplete

• I said enantiomers don’t rotate plain polarised light but why?

shortcuts

• ALWAYS complete chain of reasoning

xoxoxo

identifying the molecule that will form a chiral centre

shortcut

• look at the carbon that’s bonded to a group other than Ch3 or H — if we have no additional groups, look at every individual carbon

• bc it was asking which one will form a chiral centre - I must RMB the mechanism (how H- bonds to the carbon) adding and additional H

• therefore, I must pick a carbon that will have 3 different groups when the H is bonded to it,

• also rmb that the centre of odd chains never have a chiral centre (assuming that the molecule is symmetrical)

xoxoxo

the equation that shows the reduction of butanone

my errors

• I didn’t place the 2 infront of the [H]

• I should place brackets around the OH in the product

solution

• learn why I require 2 H for this reaction to take place

• pay great attention to detail when writing out the structural formulae (the use of brackets)

xoxoxo

By considering the mechanism of the reaction, explain why the product has no

effect on plane polarised light.

my error

• I didn’t put my answer in context - for ex, the nucleophile used (H-)

• I didn’t name the product once either - a way I could of incorporated it into my ans - the product ‘butan-2-ol’ has 2 forms of a chiral centre which means……’

• a didn’t explain a particular point - I went from ‘the product has a chiral centre.this mean it has enantiomers’ - I should of stated that this chiral centre exists in 2 forms, meaning it has 2 enantiomers

shortcuts

• always put my answer within context

• if I can explain every point, explain it

xoxo

Give the IUPAC name of the product of the reaction in part (a).

my errors

• I viewed the carbon bonded to the OH as carbon 1 instead of 2

shortcuts/solutions

• attention to detail PLS

Suggest one reason why Tollens’ reagent is used as the oxidising agent in the specific test

for aldehydes rather than the less expensive acidified potassium dichromate(VI).

my errors

• this is an AO3 synoptic question - when I come across these questions don’t EVER guess

• instead, use the information I have abt the two chemicals/ concepts - so when is it used,why is it used,how is it used,what is the chemical/concept,where is it used etc

  • flip the flashcard for the actual answer

solutions

• practice more AO3 style questions - esp in theoretical scenarios

• always use the 4Ws + how

• potassium dichromate oxidises alcohols to give a positive result

Ethanol can be oxidised by acidified potassium dichromate(VI) to ethanoic acid in a two-step

process.

ethanol - ethanal - ethanoic acid

(a) In order to ensure that the oxidation to ethanoic acid is complete, the reaction is

carried out under reflux.

Describe what happens when a reaction mixture is refluxed and why it is necessary,

in this case, for complete oxidation to ethanoic acid.

my errors

• I didn’t understand how reflux worked at all - I was not able to visualise this practical in my head

  • flip over flashcard for mark scheme

shortcut/solution

• go over the practical using chemrevise or alevel chem tutor and draw each step out — MAKE SURE I CAN VISUALISE IT

A mixture of liquids is heated to boiling point for a prolonged time

Vapour is formed which escapes from the liquid mixture, is changed back into

liquid and returned to the liquid mixture

Any ethanal and ethanol that initially evaporates can then be oxidised

Write a half-equation for the overall oxidation of ethanol into ethanoic acid.

my error

• I didnt understand how to form this half equation — use uplearn and alevel chem tutor inorder to figure this out and put this onto a flashcard

shortcut/solution

• use uplearn and alevel chem tutor inorder to figure this out and put this onto a flashcard

  
  

CH3CH2OH + H2O — CH3COOH + 4H+ + 4e–

Use these data to describe how you would obtain a sample of ethanal from a

mixture of these three compounds. Include in your answer a description of the

apparatus you would use and how you would minimise the loss of ethanal. Your

description of the apparatus can be either a description in words or a labelled

sketch

my error

• i didn’t include the thermometer when doing simple distillation.

shortcut/solution

• ALWAYS visualise the practical in my head before writing it out or drawing it

hi x

Use your knowledge of structure and bonding to explain why it is possible to

separate ethanal in this way.

my errors

• I didn’t compare the structure and bonding of ethanal to ethanoic acid and ethanol — because only writing ethanal had vDws and permanent dipole isn’t enough seen as the other 2 molecules had H bonding - that explains why ethanal evaporates first.

xoxoxox

A student obtained a sample of a liquid using the apparatus in part (c).

Describe how the student could use chemical tests to confirm that the liquid

contained ethanal and did not contain ethanoic acid.

my error

• I was unable to recall the test for carboxylic acids

• flip over to see test for COOH

shortcut

• create a diagram with alllll the tests for every chemical I need to know for alevels

• this is so I can visualise it.

Add sodium hydrogencarbonate or sodium carbonate

Result; no effervescence observed; hence no acid present