Alkenes Flashcards

1
Q

Describe the structure of alkenes?

A
  • unsaturated hydrocarbons
  • their general formula is CnH2n
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2
Q

What is a sigma bond?

A

The overlap of two orbitals consisting of a pair of electrons

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3
Q

What is a pi bond?

A
  • the overlap of two p orbitals
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4
Q

Explain the bonds in the double bond of alkenes

A
  • three out of four electrons are used in three sigma bonds to other atoms, this leaves one electron in a p oribtal
  • this forms a pi bond as the p orbitals from each carbons overlap
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5
Q

What does the P orbital make alkenes do

A

The pi bond prevents rotation around the double bond

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6
Q

What is the shape around a double bond

A

There are three areas of electron density, these repel causing a bond angle of 120 degrees

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7
Q

Define stereoisomers

A

Compounds with the same structural formula but with different arrangements of atoms in space

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8
Q

Why do stereoisomers exist?

A

You cant rotate around the carbon double bond

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9
Q

What conditions must an alkene meet to have stereoisomers?

A
  • a double carbon to carbon bond
  • different groups attached to each carbon atom of the double bond
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10
Q

What is an E isomer?

A
  • if the atoms with the highest atomic number are on opposite sides
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11
Q

What is a Z isomer?

A

Used when atoms with the highest atomic number are attached on the same side of the bond

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12
Q

Who made these priority rules?

A

Cahn - Ingold - prelog rules

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13
Q

What are cis - trans isomers?

A

Special cases of E/Z isomers where the two carbon atoms within a double bond have the same group

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14
Q

What are cis/trans isomers equivalent to ?

A

E = trans
Z = Cis

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15
Q

What are the three reactions that alkenes undergo?

A
  • Combustion
  • electrophilic addition
  • addition polymerisation
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16
Q
A
17
Q

What are the different addition reactions alkenes undergo?

A

-hydrogen
- halogens
- hydrogen halides
- steam

18
Q

What are the conditions and products of the hydrogenation of alkenes?

A
  • forms an alkane
  • nickel catalyst
19
Q

What are the products of an addition reaction of halogens with alkenes?

A
  • a dihaloalkane
20
Q

What is the test for alkanes

A
  • add bromine water to an unsaturated compound
  • the bromine reacts with the double bond, forming a haloalkane and causing a colour change from orange to colourless
21
Q

What are the products of an addition reaction of hydrogen halides and alkenes?

A
  • a haloalkane
22
Q

What are the products and conditions of steam and alkenes

A
  • an alcohol
  • requires an acid catalyst and high temps and pressures
23
Q

What is a electrophile?

A

an electron pair acceptor

24
Q

Draw the mechanism of electrophilic addition for propene and Br2

A
25
Q

What is Markownikoffs rule?

A

When a hydrogen halide reacts with an unsymmetrical alkene, the hydrogen attaches itself to the carbocation with the smallest amount of hydrogens and largest amount of carbons

26
Q

Why does the halogen attach to the carbocation with the most carbons

A
  • due to carbocation stability
  • the more alkyl groups a carbocation is attached to, the more stable it is
27
Q

describe a primary, secondary and tertiary carbocation?

A

Primary - 1 other carbon
Secondary - 2
Tertiary - 3

28
Q

How can we determine what will be major product?

A

the carbocation with the most carbons attached will be the major product

29
Q
A