3.4- alkenes Flashcards
what are alkenes (3)
-unsaturated hydrocarbons
-C=C bond is an area of high electron charge density
-bromine test orange–>colourless
what is a pi bond (2)
-restricts rotation
-they’re exposed, so electrophiles are more likely to attack
what is a sigma bond (3)
-forms overlap of the 2 electrons in 2s subshell
-stronger than pi bond due to the overlap
-longer than pi bond- nuclei can be further apart before overlap
what are stereoisomers
same structural formula, different spatial arrangement of atoms
how does geometric E-Z isomerism arise (2)
-occurs due to restricted rotation of C=C or ring shape
-both carbons in C=C must be attached to 2 different groups/atoms
how to use CIP priority rules (4)
1.consider groups on right carbon of C=C and count the total Ar of the atoms/group attached
2.repeat with left carbon
3.if both groups on same carbon have same Ar on the 1st carbon, consider the next atoms
4.atom/groups with higher Ar gets priority
what is an electrophile + give examples
electron pair acceptor
eg. Hδ+ – Brδ−
Brδ+ – Brδ−
what happens to alkenes in electrophilic addition
C=C breaks and other atoms bond to the C atoms
what happens if water is added to the product of electrophilic addition of sulphuric acid
hydrolysis reaction
produces an alcohol
what is produced in the electrophilic addition of sulfuric acid
alkyl hydrogen sulfates
conditions for electrophilic addition of sulfuric acid
cold concentrated H2SO4
why can bromine molecules react with double bonds in alkenes (2)
-C=C has a high electron charge density which induces a temporary dipole in bromine molecule
-bromine becomes polarised with δ+ and δ-
how many alkyl groups in each carbocation
primary= 1 alkyl group
secondary= 2 alkyl groups
tertiary= 3 alkyl groups
why are tertiary carbocations more stable (4)
-more alkyl groups attached to positively charged carbon atom
-alkyl groups pushes electron charge density onto the +carbon, reducing the positive charge slightly
-carbocation is more stable
-this is the positive inductive effect- it pushes electrons onto another atom
which carbocation has the largest positive charge and why
primary
-has least positive inductive effect
what are polymers
long chain molecules made from monomers
how do alkenes form polymers in polymerisation reactions
alkenes (monomers) join together after C=C is broken, to form polymers
why are addition polymers unreactive (2)
-they only have single bonds
-the main carbon chain is non-polar and is held together by VDW forces
how do plasticisers modify polymers (4)
-makes polymers more flexible by pushing the different polymer chains away from each other
-chains are further away now, so intermolecular forces are weaker
-chains can slide over each other
-polymer is now flexible and can be bent into different shapes
what is polychloroethene (PVC) used for (2)
-production of drain pipes+window frames
-PVC is hard but brittle at room temp as the polymer chains are long+packed closely together
what is polychloroethene (PVC) used for when plasticised (2)
-used in electrical cable insulation+clothing
-it is more flexible+bendy
what are plasticisers
small molecules that get between polymer chains
