DJA 5). Alkenes Flashcards Preview

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Flashcards in DJA 5). Alkenes Deck (48):
1

general formula of alkenes

CnH2n

2

whats special about alkenes

c=c (carbon-carbon double bond)
restricts rotation of groups attached (therefore E/Z isomers)

3

how many electrons does the c=c contain and what do we think of it as

4 electrons
electron dense
so has potential to attract d+ or positive ions
so is reactive

4

electrophiles are

species looking for a pair of electrons (eg H+)

5

induced dipole of Br2 by c=c

electron dense c=c 'pushes' electron density in Br2 from one side to another causing a temporary dipole

6

structure of the carbocation

positively charged ion. when the reaction is occurring the Br can attach onto carbon 1,2,3.....

7

primary secondary and tertiary structures
- how to identify

find the special bit (in our case the positive charge)
find the carbon it is related to
find how many carbons this carbon is attached to (1=primary, 2=secondary...)

8

primary secondary and tertiary structures
- which is least stable

primary

9

primary secondary and tertiary structures
- which is most stable

tertiary

10

electrophilic addition of H2SO4 to alkenes
-type of reaction
-what type of h2so4 is used
-what can happen to the product

-very exothermic
-conc h2so4 is used
-product can be converted into alcohol by addition of water (H2SO4 is reformed so has acted as a catalyst

11

test for c=c

add orange Br2 water --> decolourises

12

polymer defintion

large molecule made up of lots of repeating units called monomers

13

how to modify plastics

add plasticisers
they are small molecules that can get in between the chain of polymer, force them apart and allow them to slide over each other

14

poly(chloroethane) is also known as...

PVC

15

two types of poly(ethene)

LOPE
HOPE

16

when do you get LOPE poly(ethene)

high pressure
high temperature
produces branch chain polymers which don't pack well
molecules are flexible
uses - plastic bags, electric cables

17

when do you get HOPE poly(ethene)

just over room temp and pressure
less branching so more closely packed
molecules are inflexible
uses - crates, bottles, buckets

18

environmental issues with poly(ethene)

made from crude oil thereofre non-renewable
inert as non-polar
non biodegradable
high melting point as strong vdw between molecules

19

alcohol functional group

O-H

20

two ways to produce ethanol

direct hydration
fermentation

21

comparing direct hydration and fermentation
- rate of reaction

DH vs fermentation
fast vs slow

22

comparing direct hydration and fermentation
- cost

DH vs fermentation
expensive vs cheap

23

comparing direct hydration and fermentation
- manpower

DH vs fermentation
low vs high

24

comparing direct hydration and fermentation
- purity

DH vs fermentation
pure vs impure

25

comparing direct hydration and fermentation
- type of process

DH vs fermentation
continuous vs batch

26

comparing direct hydration and fermentation
- environmental impact

DH vs fermentation
non-renewable (ethene from crude oil) vs renewable (sugar cane)

27

direct hydration equation

h2c=ch2 + H2o --------> h3c-ch2-o-h
H3PO4

28

type of mechanism to make alcohol

electrophilic addition
see hard copy cards

29

fermentation equation

c6h12o6 ------> 2c2h5oh +2co2

30

conditions for fermentation

yeast
zymase
35 degrees
absence of air

31

what alcohol content does fermentation produce and why

up to 15%, because any greater and yeast is killed

32

what can fermentation alcohol be used for (other than to drink)

biofuel = renewable

33

why are biofuels considered carbon neutral
plus equations

a carbon neutral substance takes in as much CO2 as it produces
+6 6CO2 + 6H2O ---> C6H12O6 + 6O2 (photosynthesis)
+4 C6H12O6 -----> 2C2H5OH +2CO2 (fermentation)
+0 2x C2H5OH + 3O2 ---> 2CO2 + 3H2O (fuel is burnt)

34

why is considering biofuels as carbon neutral too simplistic

co2 will be released at many other points
extraction of glucose
fermentation (must heat to 35)
transporting raw materials

35

oxidation of alcohols
- oxidising agent (what happens to the oxidising agent and what can we see)

K2Cr2O7 /HCl
acidified potassium dichromate
it gets reduced
species that gets reduced.... (K+ is a spectator ion)
Cr2O7^2-
orange

Cr^3+ green

36

primary alcohol is oxidised...

twice

37

primary -->....--->....

primary -->aldehyde--->carboxylic acid

38

secondary --> ...

secondary -->ketone

39

tertiary-->...

not possible
no reaction

40

to make an aldehyde we use which method

distillation

41

to make a carboxylic acid we use which method

reflux

42

why do we use different methods to collect aldehydes and carboxylic acids

carboxylic acid = hydrogen bonding = high bp
aldehyde = permanent dipole forces = lower bp
so have to re-condense the aldehyde to make a carboxylic acid

43

testing for aldehydes and ketones

tollens reagent
aldehyde = silver mirror
ketone = NVC

44

testing for alcohols

add a very small piece of sodium
if gently fizzes then alcohol, if violent, water or carboxylic acid

45

another way to test for aldehydes (not tollens reagent)

Fehlings solution (blue) --> brick red precipitate

46

haloalkane test

warm then add silver nitrate
white prcipitate - chloroalkane slowest
cream precipitate - bromoalkane
yellow precipitate - iodoalkane fastest

47

carboxylic acid test

add sodium hydrogencarbonate
bubbles = carboxylic acid

48

catalyst and conditions for dehydration of alcohols

Al2O3
600 degrees c
conc H2SO4