Organic Chemistry - Top TIPS!

Question 1

If there are, for example, TWO methyl groups on the THIRD CARBON then remember ….

Answer 1

the name should include 3,3-dimethyl***

NOT JUST ONE 3.

Question 2

Explain when brackets are used in structural formula using CH(CH3) as an example

Answer 2

This means the CH3 in brackets is coming off of the same C as the one written just before in CH.

So basically you draw the thing in the brackets coming directly off of the carbon written before

Question 3

What do brackets in structural formula show?

Answer 3

that the polyatomic group inside the bracket, when drawn in displayed formula, should be attached to the nearest non-hydrogen atom on the left

Question 4

What should you write in the brackets in structural formula if you have

an ethyl group [CH2CH3] coming off of a carbon?

Two methyl groups coming off of the SAME carbon?

Answer 4

(C2H5)
Eg. CH(C2H5)

C(CH3)2

Question 5

How would you draw an ethyl group coming off of a carbon in skeletal formula?

Answer 5

>

Sideways open triangle coming off of carbon

Question 6

When drawing displayed formulas what should you always check for

Answer 6

that everything has 4 bonds!

Question 7

butylcyclohexane

Answer 7

cyclohexane with C4H9 attached - really similar to butane but one less hydrogen because it isn’t BUTANEcyclohexane, it is just BUTYLcyclohexane

Question 8

Formula for number of isomers up to and including heptane? (works for alkanes NOT ALKENES)

Answer 8

2^n - 4 +1 (where n= no. carbons)

eg. isomers of heptane = 2 to the power of 7 -4 gives 2 to the power of 3 which is 8, then +1 gives 9. So heptane has NINE ISOMERS.

Question 9

how do you read the groups on the carbon chain so you can write the name?

Answer 9

always read them so that in the name (so like 2,2,3 di-methylbutane or something) the numbers are the smallest they can be.

Question 10

How to logically draw isomers

Answer 10

Draw the main chain

Chop off a carbon and add a methyl group to as many places as possible to get different isomers

Chop of a second carbon and work out isomers with two methyl groups

chop off a third carbon and see if there is an isomer with three methyl groups

Question 11

when counting a carbon chain… (about what is on the carbon)

Answer 11

even if one of the carbons has no hydrogens attached to it, it is STILL part of the carbon chain

Question 12

when drawing chlorines onto skeletal formula…

Answer 12

don’t draw it directly at the end of the line representing the carbon, draw another mini line at another angle and then put Cl

Question 13

Give an example of a diol

Answer 13

pentan-2,3-diol

Question 14

If you are drawing a diol from an alkene then the …

Answer 14

two OHs should attach to the carbons either side of the carbon=carbon double bond

Question 15

If there is a 4 carbon chain and a methyl group AND a bromine attached to the 2nd carbon then it is called…

Answer 15

2-bromo-2-methylbutane (so the bromo first then the methyl groups)

Question 16

which mechanism involves markovnikov? And what is the rule?

Answer 16

alkene + hydrogen halide

Add the hydrogen to the carbon in the C=C that already has the most hydrogens, then the + goes on the other carbon

Question 17

If a question asks you to show three repeating units of the addition polymer formed from X…

Answer 17

• three repeating units so DON’T use brackets (these are only for showing one repeating unit when you include a C=C double bond).
• Use single bonds

Question 18

X is made from the addition polymer (w/o brackets) shown below. Give the formula of X….

Answer 18

so it would be in brackets and a double C=C of the addition polymer - this would represent it as a repeating unit because lots of those units make X

Question 19

How would you write the structural formula for a carbon with a methyl group AND another group (eg. bromine) on it?

Answer 19

CBr(CH3) - soalways write the methyl group after the other group

NOT C(CH3)Br

Question 20

How do you write the structural formula for cyclo coumpounds?

Answer 20

cyclo - (eg.)CH3CH2CH3CH2 -

Question 21

Outline how to prepare 2-brompentane in a lab?

Answer 21

heat Pentan-2-ol under reflux with 50% concentrated sulphuric acid and potassium bromide.

Question 22

In the alcohol plus halogenating agent reactions (which either produce, bromo,iodo or chloro alkanes), if you want to produce an alkane where the halogen is on a particular carbon (eg. 2-chlorobutane) then….

Answer 22

you use an alcohol where the OH is on the carbon you want the halogen to be on. So… butan-2-ol

Question 23

Two equations for ALCOHOL + IODINE + RED PHOSPHORUS reactions

Answer 23

1) P + 1.5I2 –> PI3

2) PI3 + 3C3H7OH –> 3C3H7I + H3PO3

Question 24

Two equations for ALCOHOL + POTASSIUM BROMIDE + 50% CONC SULFURIC ACID reactions

Answer 24

1) first the sulphuric acid + potassium bromide: H2SO4 + KBr –> HBr + KHSO4
2) Then the hydrogen bromide that has formed reacts with the alcohol: HBr + C5H11OH –> C5H11Br + H20

Question 25

halogenoalkane + KOH equation and ionic equation

Answer 25

halogenoalkane + KOH –> alcohol + K halogen

eg. C3H7Br + KOH –> C3H7OH + KBr

Ionic:

halogenoalkane + OH- —> alcohol + halogen (basically remove the K)

Question 26

which mechanism has three curly arrows all on one compound and where are they?

Answer 26

elimination reaction of halogenoalkanes + ethanolic KOH –> alkenes

OH- ion acts as a BASE arrow towards H on end Carbon

arrow from that C-H bond to the nearest C-C bond

arrow from the C-halogen bond to the halogen

Question 27

ammonia mechanism

Answer 27

halogenoalkane + ammonia –> primary amine

slow:
Dipole on carbon and halogen so NH3 attracts to delta + carbon and there is a curl arrow showing the halogen breaking off. Forms previous hydrocarbon with NH3 attached + the halogen that broke off

fast:
another NH3 comes in and takes a H from the already attached NH3 (first curly arrow), then one curly arrow from that H-N bond to the N. Forms a primary amine and ammonium

Question 28

Which classifications of halogenoalkane react via Sn1 and Sn2?

Answer 28

Sn1 - secondary/tertiary

Sn2 - primary/secondary

Question 29

If it says X reacts by Sn2, give the Sn1 mechanism it means that…

Answer 29

X must be secondary and can therefore either react by Sn1 or Sn2

Question 30

How to classify stuff?

Answer 30

look at the number of CARBONS attached to the carbon with the functional group attached to it

Question 31

when drawing a transition state where should the

> group that is like C3H5 go

> CH3 group go

> H go

Answer 31

> single vertical line up from central carbon
wedge at bottom
dashed line at bottom

Question 32

If the question asks you to draw the Sn1 AND Sn2 mechanisms for a secondary halogenoalkane how do you draw them?

Answer 32

SN1: with displayed formula

SN2: with wedges, dashed lines and solid lines. The negative species should be horizontal to the central carbon (solid line)

Question 33

How to write C=O in structural formula?

Answer 33

just do CO

Question 34

How to write COOH (carboxylic acid) in structural formula?

Answer 34

CO2H

Question 35

ALWAYS REMEMBER TO MAKE SURE EVERYTHING HAS

Answer 35

4 BRIAN THE OLD FUCKER BONDS ONLY

Question 36

What is the elimination equation in the section about alcohols and oxidation?

Answer 36

alcohols reacting with phosphoric acid –> alkene + water

but DO NOT include H3PO3 in the equation find out why

Question 37

How do you know when to draw intermediates of mechanisms in displayed formula or with wedges and dashed lines?

Answer 37

If the intermediate is a carbocation then draw it as displayed

If the intermediate isn’t a carbocation then draw it with dashed lines and wedges

Question 38

what do polymerisation reactions require?

Answer 38

an initiator

Question 39

if a halogenoalkane has 2+ halogens (eg. one chlorine and one fluorine) how do you decide which bond breaks in the mechanism (eg. if a bond needs to break because an OH- is substituting in)

Answer 39

the weakest bond breaks. (Fluorine is very strong so CHLORINE bond would break)

Question 40

What enables nucleophilic substitution reactions to take place?

Answer 40

the lone pair of electrons on the nucleophile

Question 41

reforming equation example C7H16 –>

Answer 41

C7H14 +H2

Question 42

general equation for

Alkane + halogen –>

Answer 42

alkane + halogen –> halogenoalkane + hydrogen halide

Question 43

What is another name for reforming?

Answer 43

dehydrogenation

Question 44

How do you know if something can be named with Cis/Trans or E/Z?

Answer 44

Look at the C=C bond, if the 4 groups are all completely different to each other then it is E/Z. But if each group on the carbon is different to its counterpart (eg. one C has a Cl and a H whilst another C has a Br and a H - so there are still H’s in common, then it is CIS/TRANS)

Question 45

If something is reacting with bromine water what will it have added to it?

Answer 45

an OH and a Br

Question 46

conditions for initiation in free radical substitution

Answer 46

UV light (photochemical reaction - reaction brought about by light)

Question 47

4 reasons why cracking of large alkanes is important in industry?

Answer 47

1) makes petrol
2) smaller chains alkane in higher demand + more useful + burn more efficiently
3) makes H2
4) recycles waste products

Question 48

free radical substitution safety precautions (3)

Answer 48

UV goggles
fume cupboard
gloves

Question 49

when drawing isomers, if you are stuck what should you do?

Answer 49

draw the carbon chain and stick the main atom (eg. a Br) onto the end/someone where you heart says to put a hydrogen and it would be really weird to put anything else (put it where it feels uncomfortable!!)