Chem Unit 2 (Alkenes) Flashcards
(43 cards)
Alkenes (homologus series so.. [2 things]
- same functional group (CnH2n)
- same structural formula (C=C)
As you increase chain length…
number of van der waals increases so melting and boiling point increases
Why are alkenes more reactive?
pi bond has delocalised electrons that are hel less tightly and attract positively-charged atoms/groups
Double bond is made up of ?
pi bond and stigma bond
Why are alkenes double-bonded?
unsaturated- can accept hydrogens (still need to make 4 single, covalent bonds, sigma binds (bond 3 atoms covalnetly) still need pi (double bond 1 pi, 1 stigma) to make 4 bonds.
Why di akenes take more energy to break?
pi bond and sigma bond brings carbon atoms closer together- held more tightky
Why can’t there be positional isomers of alkenes?
C=C bond is rigid/planar structure
atoms/grouos attached to it are fixed- so there can’t be positional isomers- Only CHAIN GEOMETRIC ISOMERS
Z isomer.. methyl groups are on..
same side of carbon atom
E isomers..methyl groups are on..
opposite side of carbon atom
What is electrophilic addition?
Electrophiles (positevely charged molecules/atoms ) accept a pair of electrons from the area of high electron density in the double bond (pi bond)
breaks the double bond > turns it intoa single bond (alkane)
Electrophilic addition: why is Bromine a dipol-dipole in the presence of..?
ethene- the double bond of the ethene induces a temporary dipole-dipole
When a hydorgen halide reacts with a unsymmetrical alkene it can make..?
diferent products becuase it depends on which end of the double bond the hakide reacts with e.g. 1-bromo-propane or 2-bromo-propane
The major prodcuct (whats mostrly formed) is going to be the secondary carbocation and the minor product the primary carbocation because?
Secondary carbocation is more stable than primary one
Order: primary>secondary>tertiary
because for primary the c+ is bonded to one other carbon atom (could be a methyl group, halogen atom) , fior secondary 2, tertiary -3
These carbon atoms donate electrons so minimise the positie charge on the carbocation, making it more stable
Add bromine water to alkenes>
alkanes>
alkenes = colourless (unsaturated) alkanes = yellow (saturated)
carbon neutral?
no net carbon emissions into the atmosphere
Making an alkene into an alcohol with sulfuric acid?
conc. H2S04 . alkene
warm it with dilut H2S04 and water > alcohol = H20
sulfuric acid is a catalyst- unchanged but sppeds up rate of reaction so is recycled.
Why is ti hydration?
overall addition of water
Hydrogenation of vegable oils condtions?
- Hydrogen
- heat to 60 degrees
Conditions for producing ehtanol by hydration (steam)
phosphoric acid catalyst- sulfuric acid too corrosive too use on a large scale
fairly low temp = 300 degrees
high pressure = 600-7000 kpa
high concentration of steam
5% intial yield but 95% with recyling of unreacted ehtene and steam
yield for ethanol isn’t 100% by hydration as?
methanol and polyethene are made as side reactions
Advantages of ethanol production by steam?
- quick
- continued recycling of ethene and steam
- no pollution
- high yield
Disadvantages if ethanol production by steam?
- crude oil (non-renewable)
- high pressure (costs)
- high temperature (costs)
polymers are
large molecule made up of thousands of monomers
momomer is..
small molecules that jon together to maje a polymer
