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Chemistry Module 4 > Alkenes > Flashcards

Alkenes Flashcards

1
Q

What are alkenes

A

unsaturated hydrocarbons

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2
Q

What types of bonds are involved in an alkene double bond

A

1 pi bond and 1 sigma bond

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3
Q

What is a sigma bond

A

formed between 2 atoms where 2 orbitals overlap each other

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4
Q

what is a pi bond

A

formed by the overlap of 2 p-orbitals

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5
Q

where is the pi bond electron density situated

A

above and below the line where the sigma bond is formed

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6
Q

why are alkenes unable to rotate around the double bond

A

pi bonds lock the carbon atoms in place

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7
Q

What angle is formed by a carbon with double bond

A

120 degrees

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8
Q

what causes a 120 degree angle to form between angles in an alkene around a carbon with a double bond

A

There are free bonds around the carbon meaning there are 3 regions of repulsion causing a 120 degree angle

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9
Q

What is stereoisomerism

A

same structural formula, different arrangement of atoms in space

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10
Q

What is E/Z isomerism

A

When rotation of atoms is restricted due to pi bonds leading to a fixed position

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11
Q

Where does EZ isomerism occur

A

in double bonded compounds where carbons are attached either side of the bond

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12
Q

Cis-Trans isomerism is what

A

when the carbon atoms are attached to methyl groups that are either opposite or the same side

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13
Q

What is more reactive, alkanes or alkanes

A

alkenes

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14
Q

what makes alkenes reactive

A

pi bonds, electrons are exposed to atoms causing it to break the double bond

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15
Q

What makes pi bonds weaker than sigma bonds

A

bond enthalpy

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16
Q

What type of reactions do alkenes undergo

A

addition reactions

17
Q

what happens in an addition reaction

A

a molecule will break the double bond of another molecule to allow the 2 reactants to form 1 product

18
Q

How does the hydrogenation of an alkene work

A

hydrogen gas reacts with the double bond of an alkene with the help of a nickel catalyst to form an alkane

19
Q

How does the halogenation of an alkene work

A

the hydrogen halide reacts with an alkene to break the alkene into an alkane with a carbocation where the hydrogen will react to help form a haloalkane

20
Q

What test can be used to test for unsaturated molecules

A

bromine water can be added

21
Q

what colour change is seen between bromine water if a C=C bond is present

A

orange —> colourless

22
Q

What is an electrophile

A

an electron pair acceptor

23
Q

What mechanism is seen in the reaction of an alkene to an alkane

A

electrophilic addition

24
Q

What mechanism is seen in the reaction of an alkene to an haloalkane

A

electrophilic addition

25
Q

What does a double bond represent

A

A region of high electron density due to pi bonds

26
Q

Describe the electrophilic addition of ethene with hydrogen gas

A
  • ethene double bond exposed to hydrogen gas forming a carbocation of ethane and hydrogen -1 ion
  • The hydrogen -1 ion will react with the carbocation double bond which will form ethane
27
Q

What partial charges are formed in H-Br

A

H has delta + charge

Br has delta - charge

28
Q

How are partial charges formed in a Br-Br molecule

A

The Br-Br molecule will come close to the double bond which causes the electrons in the Br-Br molecule to repel leading to induced dipoles forming where the has a positive and negative partial charge on each atom

29
Q

What type of bond fission occurs when a molecule reacts with a C=C bond

A

heterolytic fission

30
Q

What is a primary carbocation

A

when the carbocation is attached to 1 carbon

31
Q

what is a secondary carbocation

A

when a carbocation is attached to 2 carbons

32
Q

what is a tertiary carbocation

A

when a carbocation is attached to 3 carbons

33
Q

How can alkyl group be represented

A

-R

34
Q

What type of carbocation is the most stable

A

tertiary

35
Q

What type of carbocation is the least stable

A

primary

36
Q

what makes tertiary carbocations more stable than any other carbocation

A

the 3 carbon atoms push electrons into the carbon making it more positively charged leading to a more stable carbocation

Chemistry Module 4 (8 decks)

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