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C14- ALKENES > 14.1- ALKENES > Flashcards

14.1- ALKENES Flashcards

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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?

23
Q

According to what are the isomers names?

Study These Flashcards
A

IUPAC system using suffix -ene to indicate double bond

24
Q

What types of isomers can alkenes form? (3)

Study These Flashcards
A

chain isomers
position isomers
geometrical isomers

25
What is a position isomer for alkenes?
isomers with the double bond in different positions, that is, between a pair of adjacent carbon atoms in different positions in carbon chain
26
The longer the chain, what does this mean for the number of isomers?
more possibilities there will be so greater number of isomers
27
What are geometrical isomers a form of?
is a form of stereoisomerism
28
What do the two stereoisomers have the same of?
same strucural formula
29
What is different between the two stereoisomers?
bonds arranged differently in space
30
Where does the geometrical isomer occur?
only around C=C double bond
31
What is the isomer with the "priority" on the same side called?
Z- isomer
32
What is the isomer with the "priority" on different sides called?
E- isomer
33
How many known organic compounds are there?
a huge amount and increasing all the time
34
Why did the IUPAC produce rules for nomenclature?
so chemists agree on how isomers named
35
What was E-Z isomers first known as?
cis-trans isomerism
36
What prefixes were used instead of Z- and E- ?
cis- and trans- respectively
37
What was a disadvantage of the older notation?
did not work when there were more than two different substituents around a double bond
38
what is the E-Z notation based on?
atomic numbers
39
How are E-Z notations based on atomic number?
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
To what extent does the double bond affect the properties of alkenes?
not greatly i.e boiling + melting points
41
What are the only intermolecular forces that act between the alkene molecules?
van der Waals forces
42
As van der Waals forces are the only intermolecular forces that act between alkene molecules, what does this mean?
physical properties of alkenes very similar to those of the alkanes
43
As the number of carbon atoms increases what happens to boiling and melting point?
melting and boiling point increases
44
Are alkene soluble in water?
no
45
How does the double bond make a big difference to the reactivity of alkenes compared with alkanes? (hint- enthalpy)
bond enthalpy is much bigger
46
Are alkenes or alkanes more reactive?
alkenes
47
what does the C=C bond form in the molecule?
an electron-rich area in the molecule
48
What can the electron-rich area in the molecule be easily attacked by?
positively charged reagents
49
What are the positively charged reagents called?
electrophiles (electron liking)
50
what are electrophiles?
electron pair
51
What is an example of a good electrophile?
H+ ion
52
As alkenes are unsaturated what reactions can they undergo?
addition reactions
53
What are most of the reactions of alkenes?
electrophilic additions

C14- ALKENES (3 decks)

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