1
Q
what are halogenoalkanes + their reactivity compared to alkanes
A
halogen takes place of a H atom in an alkane
* more reactive than alkanes
2
Q
General formula of halogenoalkanes
A
CnH2n+1X
3
Q
Polarity in halogenoalkanes
A
- all C-X bonds are polar
- because halogens are more electronegative than C
- C-F most polar
- as you go down group, bonds = less polar
4
Q
halogenoalkane solubility
A
- insoluble in water (polar)
- soluble in HC (nonpolar)
5
Q
main IMF in halogenoalaknes
A
- van der waal
- dipole dipole attractions
6
Q
BP in halogenoalkanes
A
- BP increases with increased chain length
- BP increases going down halogen group
7
Q
Why does BP increase?
A
- increased van der waal
- larger molecules
- so greater no of electrons
8
Q
What decreases the MP of a homolougous series
A
- increased branching
9
Q
Which has a higher BP and why? halogenoalkanes or alkanes
A
- halogenoalkanes
- higher relative molecular masses + more polar (even if they have same chain length)
10
Q
What 2 factors determine how readily the C-X bond reacts?
A
- Cδ+-Xδ- bond polarity
- C-X bond enthalpy
11
Q
what does a nucleophile do?
A
- attack and form bonds with + or partially + carbon atoms
12
Q
bond polarity and reactivity of halogenoalkanes
A
- halogens more electronegative so polar bond
- C = partial + charge
- Halogen = partial - charge
- carbon attacked by nucleophiles
- more polar bond = more reactive
- C-I least polar + reactive
13
Q
How do bond enthalpies affect reactivity of halogenoalakens
A
- bond strength decreases going down group
- fluorine = strongest bond - small size + strong attraction
- large halogens = weaker bonds, less attraction
- weaker bonds = higher reactivity
- reactivity increases down group due to decreasing bond enthalpy
14
Q
Which is the more important factor in determining reacitivty of halogenoalkanes?
A
- bond enthalpy
15
Q
What is a nucleophile?
A
either a negatively charged ion or has an atom with a partially negative charge
16
Q
what does a nucleophile have?
A
- lone pair of electrons
- use to form a covalent bond
- lone pair is on electronegative atom
17
Q
nucleophilic substituitions
A
- nucleophiles that replace halogen in a halogenoalkane
18
Q
3 nucleophile examples
A
- hydroxide ion - oxygen has a lone pair
- cyanide ion - = carbon has lone pair
- 2 ammonia (neutral charge), nitrogen has lone pair of electrons
19
Q
what does the rate of nucleophillic substrituion depend on?
A
- halogen
- iodo most
- fluroine least
20
Q
what do curly arrows show?
A
movement of electrons
21
Q
curly arrows, hydroxide ion and chloromethane
A
- new bond forms between oxygen of hydroxide group and electron deficient carbon
- carbon can only make 4 bonds
- C-CL bond breaks
- Cl leaves as chlorine ion
22
Q
product of cyanide ion and halogenoalkane after substituition
A
- nitril with triple bonds with carbon
- leaving group
23
Q
what is the halide ion called in nucleophillic substituition?
A
- the leaving groupp
24
Q
reagent with a hydroxide ion + conditions
A
- aqeous sodium/potassium hydroxide
- slow at room temp
- so warm the mixture
- ethanol used as a solvent because halogenoalkanes dont mix with water
25
reagent with cyanide ions + conditions
* aqeous potassium cyanide
* + ethanol
* warmed
26
regeant with ammonia and conditions
* excess concentrated ammonia solution
* dissolved in ethanol
* high pressure
27
products of elimination of a halogenoalkane
* alkene
* water
* halide salt
28
conditions for nucleophillic elimination
OH ions at high temp, dissolved in ethanol
29
hydroxide ion in an elimination reaction
* acts as a base and not a nucleophile
* remove a proton
30
elimination reaction with a hydroxide ion and halogenoalkane
* hydroxide ion base uses lone pair of electrons to make a with with H
* pair of electrons used to make a bond between C + H moves between C-C atoms
* bond between C-X breaks
31
conditions of substituition vs elimination
sub = hydroxide ions are room temp, dissolved in water (aq)
elim = hydroxide ions at high temp, dissolved in ethanol
32
primary,secondary, tertiary classifications of halogenoalkanes
* where halogen atom is
* at end of chain = primary
* in the body = secondary
* at a branch = tertiary
33
type of halogenoalkaes and their reactions
* primary = substitution
* secondary = both
* tertiary - elimination
34
CFCs
halogenoalkanes containing chlorine + fluorine but no hydrogen
35
reactivity of CFCs
unreactive under normal conditions
36
uses of CFCs
* short chain = gases
* aerosol propellants
* refrigerants
* blowing agent for foam
longer chain
* dry cleaning
* de-greasing solvents
37
Reactivity of halogenoalkanes as you go up a group?
* reacitivty decreases of halogenoalkanes as u go up
* as C-X becomes stronger
38
why nucleophilic sub happens in ethanol?
haloalkanes dont dissolve in aqeueous solutions
39
What happens as CFCs rise up to ozone layer?
* due to uv light, bond breaks
* forms chlorine free radicals
* chlorine FR reacts with ozone
* repeats
40
why nucleophilic sub happens in ethanol?
haloalkanes dont dissolve in aqeueous solutions
41
elimination or substitution factors
* reaction conditions (aqeous or ethanolic solution)
* type of halogenoalkane
42
h20 asa nucleophile vs OH nucleophile
* h20 = neutral
* so poorer nucleophile
* extra step = a proton has to be lost
43
when writing the equation what form should it be in?
structural
44
when stating the leaving group, what form should it be in?
just exclude LP
include charge
45
characterisitc of a haloalkanes that allows it to undergo nucleophillic sub
* polar C-X bond
46
in substitution vs elimination, what does the nucleophile attack?
* substitution = nucleophile is attracted to partially positive charge on carbon
* elimiantion - nucleophile acts as a base and is attracted to a H+
47
reactions of halogenoalkanes
* Nucleophilic subs = nucleophile replace halogen in halogenoalkane
* Nucleophillic elimination = halogen in halogenoalkane is removed
Chemistry
flashcards
Decks in class (18)
# Cards
-
Physical - Atomic structure Y12114
-
Amount of Substance - Y1237
-
Bonding - Y12127
-
Energetics - Y1274
-
Kinetics - Y1269
-
Equilibria - Y1259
-
oxidation, reduction, redox - Y1233
-
Inorganic chemistry Periodicity - Y1241
-
Group 2, the Alkaline Earth Metals - Y1236
-
Halogens - Y1264
-
Intro to organic chemistry - Y1250
-
Alkanes - Y1287
-
Halogenoalkanes47
-
Alkenes46
-
Alcohols44
-
Organic analysis16
-
AS Paper 1 mistakes10
-
Practical Skills12
