UNIT 11 Organic Chemistry Flashcards
syllabus
- Draw and interpret the displayed formula of a molecule to show all the atoms and all the bonds
- Name and draw the displayed formulae of:
(a) methane and ethane
(b) ethene
(c) ethanol
(d) ethanoic acid
(e) the products of the reactions stated in
sections 11.4–11.7 - WHICH IS: - Name and draw the structural and displayed
formulae of unbranched:
(a) alkanes
(b) alkenes, including
but-1-ene and but-2-ene
(c) alcohols, including
propan-1-ol, propan-2-ol, butan-1-ol and
butan-2-ol
(d) carboxylic acids
containing up to four carbon atoms per molecule - Name and draw the displayed formulae of the unbranched esters which can be made from unbranched alcohols and carboxylic acids, each containing up to four carbon atoms
- State the type of compound present, given a chemical name ending in -ane, -ene, -ol, or -oic acid or from a molecular formula or
displayed formula
hydrocarbons
as chain length increases…
molecules that consist of only carbon and hydrogen atoms
boiling point INCreases.
∴ small chains = often gases, longer chains = liquids, extremely long chains = solids
a structural formula is…
an
unambiguous description of the way the atoms
in a molecule are arranged, including CH2=CH2, CH3CH2OH, CH3COOCH3
Define structural isomers
compounds with the
same molecular formula, but different structural
formulae,
including C4H10 as CH3CH2CH2CH3 and
CH3CH(CH3)CH3
and C4H8 as CH3CH2CH=CH2 and CH3CH=CHCH3
Write and interpret general formulae of
compounds in the same homologous series,
limited to:
alkanes
alkenes
alcohols
carboxylic acids
a) alkanes, CnH2n+2
(b) alkenes, CnH2n
(c) alcohols, Cn H2n+1 OH
(d) carboxylic acids, Cn H2n+1 COOH
hydrocarbons
compounds that
contain hydrogen and carbon only
petroleum (crude oil) is …
- a MIXTURE of HYDROCARBONS
- can be separated into useful fractions by FRACTIONAL DISTILLATION
- as the different hydrocarbons have different chain lengths and ∴ different boiling points
DESCRIBE: separation of petroleum into useful fractions by fractional distillation
crude oil is heated until molecules evaporate, go into heat gradient tower. Once it has produced vapor, this cools and is separated into different fractions based on their boiling point
functional group
an atom or group of atoms that determine the chemical properties of a homologous series
a homologous series is…
a family of similar compounds with similar chemical properties due to the presence of the same functional group
Describe the general characteristics of a
homologous series
(a) having the same functional group
(b) having the same general formula
(c) differing from one member to the next by
a –CH2– unit
(d) displaying a trend in physical properties
(e) sharing similar chemical properties
a saturated compound has…
molecules in which all carbon–carbon bonds are single bonds
an unsaturated compound has …
molecules in which one or more carbon–carbon bonds are not single bonds
Name the fossil fuels
coal, natural gas and
petroleum
Name methane as…
the main constituent of
natural gas
important rule about CARBON and valence electrons
carbon has 4 valence electrons
carbon always forms FOUR bonds
different formula - molecular, structural, empirical
molecular: reps the number & type of diff atoms in one molecule
structural: desc of the way the atoms in a molecule are arranged
empirical: simplest whole number ratio of the different atoms in a compound
functional groups of alkanes, alkenes, alcohol, carboxylic acid, ester
naming
general formula
e.g.s - DRAW them
alkAnes: ONLY single C-C bond
-ane
CnH2n+2
alkEnes: C=C bond
-ene
Cn H2n
alcohol: at least one –O-H group
-ol
Cn H2n+1 OH
carboxylic acid: a C=O AND an –O-H group
-oic acid
Cn H2n O2
ester: a C=O AND an –O-R group
-yl
-oate
haloalkanes
single bonds only AND at least one halogen (Cl, Br, F, I)
Cn H2n+1 X
alkynes
triple C to C bond
Cn H2n-2
amines
C-NH2
Cn H2n+1 NH2
naming organic compounds
- prefix = number of CARBONS in the longest chain
- suffix = FUNCTIONAL group
- TYPE of bonding in the carbon chain - ‘an’ (single bond) or ‘en’
- where the functional group is placed on the chain (LOWEST number possible - so e.g. going from left = 2, from right = 4. 2 lower) SO - this is the number that goes after ‘an’/’en’
pent
an
2
ol
pentan-2-ol
3 carbon chain gives prefix
1 meth-
2 eth-
3 prop-
4 but-
monkeys eat peanut butter
pent, hex, hept, oct
prop
desc bonding & properties of alkanes
- C-C and C-H bonds = COVALENT single bonds
- C and H atoms SHARE electrons to form full valence shells
what do we call this bonding
KEY WORD.
- bonding SATURATED as the carbon is bonded to the maximum number of atoms (FOUR)
chemical properties
other than COMBUSTION,
generally unreactive
combustion w/ alkanes in EXCESS O2
e.g., methane, COMPLETE
CH4 (g) + 2O2 (g) -> CO2 (g) + 2H2O (l)
- in excess oxygen, alkanes burn w/ a blue flame
- in COMPLETE combustion, form CO2 and H2O
combustion alkanes LIMITED O2
e.g., ethane, incomplete
2C2H6 (g) + 5O2 (g) -> 4CO (g) + 6H2O (l)
- in limited O2, alkanes burn w/ yellow/sooty flame
- in INcomplete combustion, form CO (+carbon/soot) AND H2O
physical properties
- COLOUR: all colourless
small chain alkanes: gases at room temp (lower BP)
- due to very weak intermolecular forces.
WHILE larger chain alkanes are liquids at room temp (higher BP)
- due to stronger intermolecular forces
+ densities between 0.6 and 0.8 g/cm3, so they are less dense than water.
substitution reaction of alkanes with chlorine / sub w/ halogens
e.g., ethane, cl2
C2H6 + Cl2 -> C2H5Cl +HCl
chloroethane
- when an atom attached to a C is replaced by another atom
- form haloalkane
- a -H atom is replaced by a halogen atom (-Cl) to form 2 new bonds: H-Cl, C-Cl.
- due to unreactive nature of alkanes, this is: a SLOW reaction + needs a UV LIGHT CATALYST.
properties of alkenes
same as alkanes
- colourless
- insoluble in water, forms 2 layers
- less dense than water
- small chain alkenes => gases
- longer chain length => liquids at room temp [stronger intermolecular forces]
addition reactions with bromine, hydrogen & steam
[CARD]
distinguish btwn saturated & unsaturated hydrocarbons by reaction with aqueous bromine
- test for saturation with Br2 [RED-BROWN]
C2H4 + Br2 => C2H4Br2
alkene goes colourless, forms a dihaloalkane
while, alkane + Br2 => remains red-brown
unsaturated bonding
the carbon is NOT bonded to the maximum number of atoms (4); [double/triple] bonds can be broken & atoms added
- alkEnes & alkynes UNSATURATED
while alkanes & alcohols are saturated.
desc manufacture of alkenes and
hydrogen by the cracking of larger alkane
molecules using a high temperature and a
catalyst
- heating the hydrocarbon molecules to around 600 – 700°C to vaporise them
- vapours then pass over a hot powdered catalyst of alumina or silica
- process breaks covalent bonds in the molecules as they come into contact with the surface of the catalyst, causing thermal decomposition reactions
- molecules are broken up in a random way which produces a mixture of smaller alkanes and alkenes
- Hydrogen and a higher proportion of alkenes are formed at higher temperatures and higher pressure
what is cracking
-
alkenes => alcohols
- addition with H2O (g) with acid catalyst
- the C=C double bond breaks and one hydrogen atom and one OH group is added to the carbons of the double bond
- the alkene has one -H atom and one -OH (hydroxyl group) added to form an alcohol
alcohols used as…
- fuels (flammable) for vehicles
- solvents (many substances soluble in short chain alcohols) - for paint varnishes
alcohol combustion - ethanol, complete combustion and burn in excess oxygen to produce carbon dioxide and water
C2H5OH (l) + 3O2 (g) → 2CO2 (g) + 3H20 (l)
4 main types of alcohol reactions
oxidation, dehydration, substitution, esterification
oxidation
- Primary alcohols can be oxidised to formaldehydeswhich can undergo further oxidation to formcarboxylicacids
- Secondary alcohols can be oxidised to formketonesonly
- Tertiary alcohols do not undergo oxidation
- The oxidising agents of alcohols includeacidified K2Cr2O7oracidified KMnO4
dehydration
undergo this to form?
what happens?
-alcohols undergodehydrationto form alkenes
- Alcohol vapour is passed over ahot catalystof aluminium oxide (Al2O3) powder OR pieces of porous pot or pumice as well as concentrated acid can be used as catalysts
define dehydration reaction
- a type ofeliminationreaction
- a reaction in which a water molecule is removed from a larger molecule
e.g.
Ethanol (C₂H₅OH) → Ethylene (C₂H₄) + Water (H₂O)
substitution of alcohols
- ## replaced by?
- In thesubstitutionof alcohols, a hydroxy group (-OH) is replaced by a halogen to form anhalogenoalkane
- can be achieved by reacting the alcohol with:
📍 HX (rather than using HBr, KBr is reacted with H2SO4or H3PO4to make HBr that will then react with the alcohol)
📍 PCl3and heat
📍 PCl5at room temperature
📍 SOCl2
esterification
-condensationreaction between a carboxylic acid and an alcohol to form anester and a water molecule
- carboxylic acid and alcohol areheated under refluxwith astrong acid catalyst(such as H2SO4or H3PO4)
- Carboxylic acid + alcohol → ester + water
- The reaction is reversible so an equilibrium mixture can be established with all the reactants and products
-Esters havesweet,fruity smells
