Organic Flashcards
What is the bond angle in alkanes?
109 1/2 °
What is the equation for calculating the percentage composition of an element?
% composition = (mass of all the atoms of that element in the molecule/ relative molecular mass) x 100
What is empirical formula?
The simplest whole-number ratio of the atoms in a molecule
What is the general formula of an alkane?
CnH2n +2
What is the general formula for an alkene?
CnH2n
What is the general formula for alkynes?
CnH2n -2
What is the general formula for cycloalkanes?
CnH2n
What is the general formula for cycloalkenes?
CnH2n -2
What are the steps of combustion data calculations?
1/ Divide grams of CO2 and H2O produced by their respective molecular mass
2/ Times the calculated amount of H2O by 2 as there are two atoms of H
3/ Divide by the smallest amount of the new totals. This should give a ratio
4/ Convert the ratios into whole-number forms by multiplying by an appropriate amount
4/
What is the equation for combustion of methane?
CH4(g) + 2O2(g) –> CO2(g) + 2H2O(g)
What are the two possible products, besides water, of the partial combustion of methane?
CO(g) and C(s)
What type of reaction is the splitting up of two molecules of the same element?
Homolytic fission
What is cracking?
The breaking down of a large chained alkane into a smaller chain alkane and an alkene
What are alkenes?
Unsaturated hydrocarbons with a π bond
What is the bond angle in alkenes?
120°
Why do alkenes have geometrical isomerism?
There is a lack of free rotation about the π bond when there are two different groups at each end of the double bond
H H
\ /
C = C
/ \
Cl Cl
What type of geometrical isomerism is this?
Cis / Z
H Cl
\ /
C = C
/ \
Cl H
What type of geometrical isomerism is this?
Trans / E
Give an equation for the hydrogenation of propene?
What is the catalyst for this reaction?
C3H6 + H2 —> C3H8
Nickel
What are the conditions for addition of HX to an alkene?
Room temperature
Concentrated solution of HX
What kind of reaction is the addition of HX to an alkene?
Electrophilic addition
Conditions for reacting an alkene with Br2
Give an equation and what this can be used to test for
Room temperature
C2H4 + Br2 –> C2H4Br2
Can test for the presence of a C=C bond
What is unusual about the reaction of Br2 with an alkene compared to the same reaction with chlorine?
A bride forms when using Br2 so the mechanism is slightly different
What is Markornikoff’s rule and what does it apply to?
The reaction of HX with an alkene
- The hydrogen of HX adds to the carbon which already has the most hydrogens
If Cl2 is non-polar, how does it react with an alkene?
The Cl2 becomes polarised as it approaches the electron rich double bond
What are the conditions for an alkene reacting with water?
What does it produce?
Give an equation
- Water must be as steam
- 600K
- 6 Mpa (60 atm)
- Catalyst of H3PO4 (phosphoric acid)
- inert support
An alcohol
C2H4 + H2O —> CH3CH2OH
How would you synthesise a haloalkane from an alkene?
Give an equation
React with conc. HX at room temperature
C2H4 + HBr —> CH3CH2Br
What are the equations for synthesising a halogenoalkane from an alcohol?
CH3CH2OH + HBr —> CH3CH2Br + H20
3CH3CH2OH + PI3 —> 3CH3CHI + H3PO3
CH3CH2OH + PCl5 —> CH3CH2Cl + POCl3 + HCl
CH3CH2OH + SOCl2 —-> CH3CH2Cl + SO2 + HCl
How would you synthesise an alcohol from a halogenoalkane?
Give an example
Stir the halogenoalkane with dilute aqueous alkali at room temperature
H2O
CH3CH2Br + NaOH ——–> CH3CH2OH + NaBr
What is the reactivity order for carbons bonded to a halogen?
C-I > C-Br > C-Cl»_space; C-F
What are the characteristics of an SN2 reaction?
- occurs in primary and some secondary halogenoalkanes but not tertiary
Rate ∝ [RX] [Nucleophile]
Both the RX and the nucleophile are involved in the rate determining step
Which is faster: SN1 or SN2?
SN1
What are the characteristics of an SN1 reaction?
Fast
Rate ∝ [RX]
Only the concentration of the halogenoalkane is involved in the rate determining step
Can produce stereoisomers if halogenoalkane is chiral
When are SN1 reactions favoured?
Favoured in tertiary molecules
When using polar protic solvents
When are SN2 reactions favoured?
In primary molecules
When using polar aprotic solvents
What are non-polar aprotic solvents?
Give an example
- Do not contain polar O-H or N-H groups
- Hydrocarbons
What are polar aprotic solvents?
Give examples
Polar molecules that cannot hydrogen bond
- CH3CN
- Me2CO
- DMF
- DMSO
What are polar protic solvents?
Give examples
Contain polar O-H or N-H groups and can hydrogen bond
- H2O
- CH3CH2OH
- Liquid NH3
Describe the conditions for reacting a halogenoalkane with ammonia
Give an equation
- heat the halogenoalkane with excess ammonia in an ethanolic solution
CH3CH2OH CH3CH2BR + NH3 -------------------> CH3CH2NH2 + HBr
This produces an amine
What are the conditions for reacting a halogenoalkane with cyanide?
What type of reaction is it?
Give an equation
- Heat the halogenoalkane with an alcoholic KCN solution
Substitution (techniqely addition)
(CH3)2 CHBr + KCN —–> (CH3)2 CHCN + NaBr
What can the product of reacting a halogenoalkane alkane with cyanide be reduced to?
Give an equation
A primary amine
(CH3)2CHCN —-> (CH3)2CHCH2NH2
Describe the elimination reactions of halogenoalkanes
- Involve heating the halogenoalkane with concentrated ethanolic alkali
- HX is removed from the molecule
NaOH/C2H5OH CH3CH2Br ------------------------> C2H4 + CH3CH2OH + Br- Reflux
Describe the E2 reaction
Give the rate equation
- Bonds make and break at the same time
Rate ∝ [RX] [BASE]
Describe the E1 reaction
Give the rate equation
- bonds make and break in different steps
- Most substituted alkene is the favoured product
- E-isomers are favoured on steric grounds
Rate ∝ [RX]
When are elimination reactions favoured?
- using alcoholic solutions
- high temperatures
- using secondary or tertiary halides
- using polar solvents
Give the general equation of the reaction of a halogenoalkane with silver nitrate solution
RX + H2O —-> ROH + H+ + X-
Ag + X- ——> AgX(s)
Describe the different reactions of halogenoalkanes reacting with AgNO3 solution
1-chlorobutane slow white (AgCl)
1-bromobutane medium cream (AgBr)
1-iodobutane fast yellow (AgI)
What are the physical properties of alcohols?
- Very polar O-H bonds
- Hydrogen bonding leads to high boiling temperatures
- Ethanol is miscible with water but from butanol upwards, alcohols are not miscible
Describe the reaction of fermentation
Give an equation
- Anaerobic
- requires yeast
- 35°C
C6H12O6 ——> 2CO2 + 2C2H5OH
How would you produce a halogenoalkane from an alcohol?
Give all equations
Heat with a mixture of NaBr and conc. H2SO4
NaBr + H2SO4 —–> NaHSO4 + HBr
CH3CH2OH + HBr ——-> CH3CH2BR + H2O
Give all of the equations of ethanol reacting with phosphorus halides
3 CH3CH2OH + PCl3 —–> 3 CH3CH2Cl + H3PO3
CH3CH2OH + PCl5 ———> CH3CH2Cl + POCl3 + HCl
3 CH3CH2OH + PBr3 ——-> 3 CH3CH2Br + H3PO3
3 CH3CH2OH + PI3 ——–> 3 CH3CH2I + H3PO3
Describe a test for an OH group
Give an equation
What can be observed?
Reacting an alcohol with PCl5
CH3CH2OH + PCl5 —–> CH3CH2Cl + POCl5 + HCl
White, misty fumes
Describe a reaction of ethanol with SOCl2
Reacts at room temperature
CH3CH2OH + SOCl2 ——> CH3CH2Cl + HCl + SO2
Misty fumes of HCl and SO2 can be seen
Give an equation for the reaction of ethanol with sodium
2 CH3CH2OH + 2Na —–> 2 CH3CH2O- Na+ (s) + H2
How would you form an alkene from an alcohol?
Dehydration reaction
Pass alcohol over hot Al2O3 at 400°C
Heat with excess conc. H2SO4
CH3CH2OH —-> C2H4 + H2O
How would you produce an ester from an alcohol?
Give an equation
Heat with a carboxylic acid
Acid catalyst (conc. H2SO4)
CH3CH2COOH + CH3CH2OH CH3CH2COOCH2CH3
+ H2O
How are esters named?
1st part from the alcohol
2nd part from the acid
eg ethyl propanonate
What are the benefits of using an acyl chloride to produce an ester?
- reacts in the cold
- reaction isn’t reversible
Give the equation for the production of an ester using an acyl chloride
CH3COCL + CH3CH2OH —-> CH3COOCH2CH3 + HCl
How would you oxidse an alcohol?
What will you see?
Use acidified potassium dichromate (VI) solution (K2Cr2O7/H2SO4)
Colour change from orange to green
How would you produce an aldehyde from an alcohol?
Give the equation
Use PCC in CH2Cl2 solution
PCC/CH2CL2 CH3CH2OH ----------------------- CH3CH2O
