Organic Chemistry - Top TIPS! Flashcards
If there are, for example, TWO methyl groups on the THIRD CARBON then remember ….
the name should include 3,3-dimethyl***
NOT JUST ONE 3.
Explain when brackets are used in structural formula using CH(CH3) as an example
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
What do brackets in structural formula show?
that the polyatomic group inside the bracket, when drawn in displayed formula, should be attached to the nearest non-hydrogen atom on the left
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?
(C2H5)
Eg. CH(C2H5)
C(CH3)2
How would you draw an ethyl group coming off of a carbon in skeletal formula?
>
Sideways open triangle coming off of carbon
When drawing displayed formulas what should you always check for
that everything has 4 bonds!
butylcyclohexane
cyclohexane with C4H9 attached - really similar to butane but one less hydrogen because it isn’t BUTANEcyclohexane, it is just BUTYLcyclohexane
Formula for number of isomers up to and including heptane? (works for alkanes NOT ALKENES)
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.
how do you read the groups on the carbon chain so you can write the name?
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.
How to logically draw isomers
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
when counting a carbon chain… (about what is on the carbon)
even if one of the carbons has no hydrogens attached to it, it is STILL part of the carbon chain
when drawing chlorines onto skeletal formula…
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
Give an example of a diol
pentan-2,3-diol
If you are drawing a diol from an alkene then the …
two OHs should attach to the carbons either side of the carbon=carbon double bond
If there is a 4 carbon chain and a methyl group AND a bromine attached to the 2nd carbon then it is called…
2-bromo-2-methylbutane (so the bromo first then the methyl groups)
which mechanism involves markovnikov? And what is the rule?
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
If a question asks you to show three repeating units of the addition polymer formed from X…
- 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
X is made from the addition polymer (w/o brackets) shown below. Give the formula of X….
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
How would you write the structural formula for a carbon with a methyl group AND another group (eg. bromine) on it?
CBr(CH3) - soalways write the methyl group after the other group
NOT C(CH3)Br
How do you write the structural formula for cyclo coumpounds?
cyclo - (eg.)CH3CH2CH3CH2 -
Outline how to prepare 2-brompentane in a lab?
heat Pentan-2-ol under reflux with 50% concentrated sulphuric acid and potassium bromide.
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….
you use an alcohol where the OH is on the carbon you want the halogen to be on. So… butan-2-ol
Two equations for ALCOHOL + IODINE + RED PHOSPHORUS reactions
1) P + 1.5I2 –> PI3
2) PI3 + 3C3H7OH –> 3C3H7I + H3PO3
Two equations for ALCOHOL + POTASSIUM BROMIDE + 50% CONC SULFURIC ACID reactions
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
halogenoalkane + KOH equation and ionic equation
halogenoalkane + KOH –> alcohol + K halogen
eg. C3H7Br + KOH –> C3H7OH + KBr
Ionic:
halogenoalkane + OH- —> alcohol + halogen (basically remove the K)
which mechanism has three curly arrows all on one compound and where are they?
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
ammonia mechanism
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
Which classifications of halogenoalkane react via Sn1 and Sn2?
Sn1 - secondary/tertiary
Sn2 - primary/secondary
If it says X reacts by Sn2, give the Sn1 mechanism it means that…
X must be secondary and can therefore either react by Sn1 or Sn2
How to classify stuff?
look at the number of CARBONS attached to the carbon with the functional group attached to it
when drawing a transition state where should the
> group that is like C3H5 go
> CH3 group go
> H go
> single vertical line up from central carbon
wedge at bottom
dashed line at bottom
If the question asks you to draw the Sn1 AND Sn2 mechanisms for a secondary halogenoalkane how do you draw them?
SN1: with displayed formula
SN2: with wedges, dashed lines and solid lines. The negative species should be horizontal to the central carbon (solid line)
How to write C=O in structural formula?
just do CO
How to write COOH (carboxylic acid) in structural formula?
CO2H
ALWAYS REMEMBER TO MAKE SURE EVERYTHING HAS
4 BRIAN THE OLD FUCKER BONDS ONLY
What is the elimination equation in the section about alcohols and oxidation?
alcohols reacting with phosphoric acid –> alkene + water
but DO NOT include H3PO3 in the equation find out why
How do you know when to draw intermediates of mechanisms in displayed formula or with wedges and dashed lines?
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
what do polymerisation reactions require?
an initiator
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)
the weakest bond breaks. (Fluorine is very strong so CHLORINE bond would break)
What enables nucleophilic substitution reactions to take place?
the lone pair of electrons on the nucleophile
reforming equation example C7H16 –>
C7H14 +H2
general equation for
Alkane + halogen –>
alkane + halogen –> halogenoalkane + hydrogen halide
What is another name for reforming?
dehydrogenation
How do you know if something can be named with Cis/Trans or E/Z?
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)
If something is reacting with bromine water what will it have added to it?
an OH and a Br
conditions for initiation in free radical substitution
UV light (photochemical reaction - reaction brought about by light)
4 reasons why cracking of large alkanes is important in industry?
1) makes petrol
2) smaller chains alkane in higher demand + more useful + burn more efficiently
3) makes H2
4) recycles waste products
free radical substitution safety precautions (3)
UV goggles
fume cupboard
gloves
when drawing isomers, if you are stuck what should you do?
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!!)
