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C14- ALKENES > 14.1- ALKENES > Flashcards

14.1- ALKENES Flashcards

1
Q

What type of hydrocarbons are alkenes?

A

unsaturated

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2
Q

What are alkenes made up of?

A

carbon and hydrogen only

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3
Q

What do alkenes have that make them alkenes?

A

one or more carbon-carbon double bonds

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4
Q

What does the double bond in alkenes mean to the number of hydrogens?

A

alkenes have fewer than the maximum possible number of hydrogen atoms

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5
Q

What property does the double bond give alkenes?

A

makes them more reactive than alkanes

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6
Q

Why are alkenes more reactive than alkanes?

A

because of the high concentration of electrons (high electron density) between the two carbon atoms

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7
Q

What is ethene used for?

A

as the starting material for a large range of products

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8
Q

What products can be formed from ethene? (4)

A

polymers:
polythene, PVC, polystyrene and terylene fabric

products:
antifreeze and paints

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9
Q

When is alkenes produced in large quantities?

A

when crude oil is thermally cracked

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10
Q

What is the general formula for alkenes?

A

CnH2n

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11
Q

What is the shape of ethene?

A

planar (flat) molecule

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12
Q

What happens to the angles as ethene is a planar molecule?

A

makes the angles between each bond roughly 120 degrees

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13
Q

Unlike the C-C bond in alkanes, what is there none of in alkenes?

A

no rotation about the double bond

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14
Q

Why is there no rotation about the double bond?

A

due to the make up of the double bond

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15
Q

What happens to the shape if any molecules in which a hydrogen atom in ethene is replaced by another atom or group?

A

it will have the same flat shape around the carbon-carbon double bond

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16
Q

as well as a normal C-C single what else is there?

A

there is a p-orbital on each carbon

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17
Q

what does each p-orbital contain?

A

contains a single electron

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18
Q

What do the two orbitals on the carbons do?

A

overlap to form an orbital with a cloud of electron density above and below the single bond

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19
Q

What is the name of the orbital formed from the two p-orbitals overlap?

A

called a π-orbital

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20
Q

What does the presence of of the π-orbital mean?

A

means the bond cannot rotate

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21
Q

What is it sometimes called when the bond cannot rotate?

A

restricted rotation

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22
Q

What can alkenes with more than 3 carbons form?

A

isomers

23
Q

According to what are the isomers names?

A

IUPAC system using suffix -ene to indicate double bond

24
Q

What types of isomers can alkenes form? (3)

A

chain isomers
position isomers
geometrical isomers

25
Q

What is a position isomer for alkenes?

A

isomers with the double bond in different positions, that is, between a pair of adjacent carbon atoms in different positions in carbon chain

26
Q

The longer the chain, what does this mean for the number of isomers?

A

more possibilities there will be so greater number of isomers

27
Q

What are geometrical isomers a form of?

A

is a form of stereoisomerism

28
Q

What do the two stereoisomers have the same of?

A

same strucural formula

29
Q

What is different between the two stereoisomers?

A

bonds arranged differently in space

30
Q

Where does the geometrical isomer occur?

A

only around C=C double bond

31
Q

What is the isomer with the “priority” on the same side called?

A

Z- isomer

32
Q

What is the isomer with the “priority” on different sides called?

A

E- isomer

33
Q

How many known organic compounds are there?

A

a huge amount and increasing all the time

34
Q

Why did the IUPAC produce rules for nomenclature?

A

so chemists agree on how isomers named

35
Q

What was E-Z isomers first known as?

A

cis-trans isomerism

36
Q

What prefixes were used instead of Z- and E- ?

A

cis- and trans- respectively

37
Q

What was a disadvantage of the older notation?

A

did not work when there were more than two different substituents around a double bond

38
Q

what is the E-Z notation based on?

A

atomic numbers

39
Q

How are E-Z notations based on atomic number?

A

look at atoms attached to each of the carbon atoms in double bond
when two atoms of higher atomic number on same side of C=C, isomer described as Z

40
Q

To what extent does the double bond affect the properties of alkenes?

A

not greatly i.e boiling + melting points

41
Q

What are the only intermolecular forces that act between the alkene molecules?

A

van der Waals forces

42
Q

As van der Waals forces are the only intermolecular forces that act between alkene molecules, what does this mean?

A

physical properties of alkenes very similar to those of the alkanes

43
Q

As the number of carbon atoms increases what happens to boiling and melting point?

A

melting and boiling point increases

44
Q

Are alkene soluble in water?

A

no

45
Q

How does the double bond make a big difference to the reactivity of alkenes compared with alkanes? (hint- enthalpy)

A

bond enthalpy is much bigger

46
Q

Are alkenes or alkanes more reactive?

A

alkenes

47
Q

what does the C=C bond form in the molecule?

A

an electron-rich area in the molecule

48
Q

What can the electron-rich area in the molecule be easily attacked by?

A

positively charged reagents

49
Q

What are the positively charged reagents called?

A

electrophiles (electron liking)

50
Q

what are electrophiles?

A

electron pair

51
Q

What is an example of a good electrophile?

A

H+ ion

52
Q

As alkenes are unsaturated what reactions can they undergo?

A

addition reactions

53
Q

What are most of the reactions of alkenes?

A

electrophilic additions

C14- ALKENES (3 decks)

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