Alkenes Flashcards by Zaara Unknown

what is the general formula of alkenes?

CnH2n

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What is a sigma bond

a bond formed by the lengthways overlap of orbitals directly between 2 bonding atoms

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what is a pi bond?

the sideways overlap of a spare unbonded p orbital present on each carbon atom in the double bond

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what forms a pi bond

overlap produces a cloud of electron density above and below the molecule

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What shape and angle is the double C=C bond

Planar
120°
because no free rotation around the double bond

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what is structural isomerism

molecules with the same molecular formula but different structural formula

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what is stereoisomerism

molecules with the same structural formula but different arrangement of atoms in space

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what is a Z isomer

when the functional groups are on the same side of the carbon eg both on top or both on the bottom
Zame side

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How does geometric isomerism occur

restricted rotation around the double bond
2 different groups are bonded to each C atom in the C=C

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When does E isomerism occurs

when the functional groups are on different sides
eg one top left and one bottom right
(opposite)

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What are cis isomers

when the same functional groups are on the same side
eg 2 CH3 on the top

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what are trans isomers

the same functional groups on opposite sides
eg CH3 top left and CH3 bottom right

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What are the 4 addition reactions of alkenes?

Hydrogenation
Halogenation
Addition of an acid
Hydration

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What is hydrogenation and what reagents are required for it

Addition of hydrogen
Reagents : H2 (gas) or Nickel
Double bond breaks and Hydrogen added

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What is the importance of hydrogenation

used in the manufacture of margarine

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What is halogenation and what are the reagents for it

Addition of a halogen
Regents : Br2 or Cl2
Double bond breaks and Br - Br or Cl-Cl added

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What is the importance of halogenation

used in the test tube lab test for the presence of an alkene

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What are the reagents required for the addition of an acid

HBr or HCl

what is the importance of adding an acid

used in organic synthesis when making a haloalkane

What is hydration and what are the reagents required

Addition of water
Reagents : steam/temp > 100
and Catalyst : H2SO4 or H3PO4

What is the importance of hydration

used to make industrial ethanol for fuel and solvent purposes

What is an electrophile

an electron pair acceptor

What is the electron dense region

The C=C bond is a region of high electron density and attracts electrophoresis
Also attracts delta positive

What happens when the C=C bond breaks in electrophilic addition

the alkenes undergo addition reactions and form a single bond
This allows each carbon atom to form a bond with other atoms forming saturated (single bonds) C-C products

Step 1 for electronic addition

curly arrow from double bond to delta positive atom

Step 2 for electrolytic addition

curly arrow from bond between X-Y to delta negative (Y)

step 3

double bond breaks C carbocation formed : + on the carbon bonded to more carbons :Y- becomes a nucleophile

step 4

curly arrows from :Y- electron pair to carbocation Y added to the carbocation

how do u test for alkenes (unsaturated compounds) (double bonds)

when alkenes are added to bromine water a yellow colour is recolonised this shows the presence of a C=C double bond

how does Br2 become polar for electrophilic addition

electron dense area of the carbon double bind induces a dipole ok the bromine molecule it repels the electrons in the Br-Br so it becomes polar

How many products are formed from an unsymmetrical alkene

2 major and minor product

When is the major product formed

Major product is formed via the most stable cation (tertiary) Most stable cation = carbon bonded to the most other carbons

when is the minor product formed

from the least stable carbocation

what is addition polymerisation

joining monomers (alkenes) to form polymers (poly(alkenes) which are unreactive unreactive because the C-C bind is single and non polar

how do y draw a repeating unit

double bond broken extended bonds sticking out the side brackets n outside the brackets n = number of repeating units

what can waste polymers be used for

recycled/reused but not all 2 alternatives to recycling plastics

What is combustion for energy production

polymers burned to release heat energy for generating electricity Adv : reduced the need for combusting fossil fuels Dis : combustion of chlorine containing pointed produce HCL gas which is toxic and corrosive Releases CO2 - global warming Releases toxic CO

what is PVC

poly chloro ethene hard, rigid because permanent dipole dipole forced between chains due to delta position and negative Cl

How is PVC made more flexible

Plasticisers are added to the PVC to reduce the effectiveness of these attractions

what are the problems with plastics

non biodegradable due to strong non polar C-C bonds

How can HCL gas be prevented from entering the atmosphere

reacting it with bases eg CaCO3 or CaI to neutralise it

how to minimise the dangers of toxic CO

entire there’s plenty of oxygen to prevent incomplete combustion

what is organic feedstock

raw materials for making chemicals advantage : reduces the need for cracking crude oil