Chapter 13 Alkenes Flashcards
(24 cards)
What are alkenes?
Unsaturated hydrocarbons containing at least one C=C
3 of the 4 electrons are used in the sigma bonds
What is a pi bond?
Lone electron is in the p-orbital, forming a pi-bond overlapping sideway, one from each carbon atom of the double bond
pi-electron density is concentrated above and below the line joining the nuclei of the bonding atoms
Has two carbon atoms in position and prevents rotating around the double bond
What is the shape of alkenes?
Trigonal planer, 3 regions repel each othr as far as possible
Bond angle 120
What is steroisomerism?
Tha same structural formula but a different arrangement of atoms in space
What is E/Z isomerism?
Only occurs in compounds with C=C and has different groups attached to each carbon atom
What are Z isomers?
Groups of higher properties on the same side of carbon chains
What are E isomers?
Groups of higher priorities on oppistie sides of the carbon chain
What is cis/trans isomerism?
Have hydrogen atoms on each carbon in the double bond
What are cis isomers?
Hydrogen atoms on the same side of the carbons
What are trans isomers?
Have hydrogen atoms on oppisite side of the carbons
How is priority determined?
The higher the atomic number, the higher the priority
Why are alkenes more reactive than alkanes?
The presence of the pi-bond, pi-electrons are more exposed, readily breaks
What is hydrogenation?
When alkene is mixed with hydrogen and passed over a nickel catalyst at 423K to form an alkane
How can we determine alkenes?
Reaction with bromine, which decolarises bromine water
What is the reaction of alkenes to form haloalkenes?
React with hydrogen halides at room temperature
What is the reaction of alkenes to form alcohols?
Alkenes react with steam in the presence of phosphoric acid catalyst
What is the mechanism for alkenes?
Electrophilic addition, which the high electron density attracts electrophiles
What are electrophiles?
An atom or a group of atoms that is attracted to an electron-rich centre and accepts an electron pair
Usually a positive ion or a molecule containing partial positive charge
What are corbocations?
Classified by the number of alkyl groups attached to the positively charged carbon atom
What is the most stable carbocation?
Tertiary cations, as they pushes electrons towards the positive charge of the carbocation, and the positive charge is spread over the alkyl groups, making the ion more stable
How can we reduce the affect of polymers?
Recycling polymers conserves finite fossil fuels as well as decreasing the wast going to landfill
PVC is recylced and recovered by precipitatin from the solvent
Waste polymers can be incinerated to produce heat and producing electricity
Feedstock recycling is the chemical and thermal processes that can reclaim monomers from waste polymers
What are bioplastics?
Produced from plant starch, cellulose, plant oils and proteins offer a renewable and sustainable alternative to oil-based products
What are biodegradable polymers?
Broken down by microorganisms into water, carbon dioxide and biological compounds
What are phtodegradable polymers?
Contain bonds that are weakend by absorbing light to start the degradation
