2.4/ 2.5 Flashcards
What is a structural isomer?
Same molecular formula, but different structural formula
Definition of a radical
Species containing an unpaired electron.
Definition of a electrophile
Electron deficient species that is attracted to electron rich species e.g Br2, Cl2, H-Br (accepts electrons)
Definition of a nucleophile
Electron rich specie that is attracted to electron deficient species e.g. -OH, -CN, (donates electrons)
meaning of the term saturated
Maximum number of H atoms/only single covalent bonds.
Suggest why a branched chain isomer has a lower boiling point than a straight chain.
Branched chain have lower surface area. Therefore, less induced dipole-id forces between molecules. Therefore, lower boiling point.
What type of isomer is but-1-ene compared to but-2-ene
Positional isomers since the position of the double bond has changed.
Test for an alkene
Add aqueous bromine, electrophillic addition reaction. Orange brown turns to colourless.
Define heterolytic fission
The breaking of a covalent bond where one atom takes both electrons from the bond, forming a cation and anion
what is stage one of free radical substitution?
initiation stage
what occurs In the initiation stage?
atom of an element (e.g chlorine) will undergo homolytic fission which produces a free radical.
what is stage two of free radical substitution?
propagation stage
what happens during the propagation stage?
C2H6 + Cl. → .CH2CH3 + HCl
chain reactions occur where the free radicals will react until they have replaced all hydrogen atoms from the carbon atom.
the free radical will attack a hydrogen atom and removes it from the carbon which creates a carbon radical next to the carbon and a new atom of hydrogen Cl for example
the carbon radical then reacts with the excess Cl to add a Cl to the carbon but also creates new one
what is stage three of free radical substitution?
termination stage
what happens during the termination stage?
two free radicals react together which can increase length of carbon chain
.CH2CH3 + Cl. → CH2ClCH3
what condition is required for the initiation stage?
UV light must be present
what type of bonds are present in alkenes?
double bonds = pi bonds 𝛑
single bonds = sigma bonds o~
what bonds are present between one carbon and one hydrogen?
single, sigma bonds
describe bonding between carbon atoms and ethene
carbon atoms are double bonded together by pi bonds which shows the overlap of p orbitals and the carbons are also single bonded to two hydrogens each with sigma bonds which show an overlap of s orbitals
what orbital does a pi bond signify?
p-obital
what orbital does a sigma bond signify?
s-orbital
what reactions do all alkenes undergo?
electrophilic addition reactions
what is step one to do in this reaction?
identify the electrophile and the nucleophile, place sigma o~+ and o~- next to them. draw a curly arrow to the negative charged element to show movement of electrons and a curly arrow pointing at the positive charged element signifying it has joined the compound
what happens in step two of this reaction?
after the positive element has joined the atom the negatively charged one gains two electrons and shows a full minus charge. a carbon in the main compound will have a full plus by it to attract the negative element
what is step three of this reaction?
the remaining negative element joins the main compound on where the positive carbon was
if electrophilic addition produces more than one possible product, which do we use and why?
the major product which is the carbocation with the most alkyl groups (CH3). this is because if for example it joins onto a propene then putting the extra element e.g Br onto carbon two will mean it will have two alkyl groups to stabilise it
what are the different carbocations?
- primary - bonded to the first carbon
secondary - bonded to the second carbon
tertiary - bonded to the third carbon
what are the standard conditions of hydrogenation?
temperature of 150c
nickel catalyst
H2 available
what process do alkenes under go that is poly
addition polymerisation
names of ethene after being polymerised
poly ethene (always add poly at start)
draw the repeating unit of tetrafluroethene and name it -
polytetrafluroethene
how to calculate empirical formula using C4H5Cl
divide using smallest number, in this case one, so it remains C4H5Cl
calculate empirical formula of C6H12
divide all by 6 so it would become CH2
does a double bond contain high electron density and high negative energy?
yes
calculate empirical formula using percentages.
firstly divide percentages by the elements atomic mass e.g carbon = 12
then this will give you the mols present in each element
use the smallest number of mols and use that number to divide the other mols by this one
this will give you a set of numbers e.g 1,1 and 2
so you would write XY2Z
Why does E-Z isomerism occur?
restricted rotation about the planar carbon carbon double bond
where are the priority groups on a z isomer?
on the same side going across (at top across or at bottom across)
on the opposite side going across
on the opposite side going across
