Organic 1st yr Flashcards
Functional group
is an atom or group of atoms which when present in different molecules causes them to have similar chemical properties
Homologous series
Homologous series are families of organic compounds with the same functional group and the same general formula.
- They show a gradual change in physical properties (e.g. boiling point).
- Each member differs by CH2 from the last.
- same chemical properties
Order of priority highest first:
CA, ALD, KET,halo, alke,alc
Carboxylic acids >aldehydes>ketones>alcohols>alkenes>halogenoalkanes
HOMOLYTIC FISSION
each atom gets one electron from the covalent bond
When a bond breaks by homolytic fission it forms two Free Radicals. Free Radicals do not have a charge and are represented by a
A Free Radical is a reactive species which possess an unpaired electron
HETEROLYTIC FISSION
one atom gets both electrons
Structural isomers
same molecular formula different structures (or structural formulae)
Chain isomers
Compounds with the same molecular formula but different structures of the carbon skeleton
position isomers
Compounds with the same molecular formula but different structures due to different positions of the same functional group on the same carbon skeleton
Functional group isomers
Compounds with the same molecular formula but with atoms arranged to give different functional groups
Stereoisomerism
Stereoisomers have the same structural formulae but have a different spatial arrangement of atoms
E-Z stereoisomers arise when:
ab
(a) There is restricted rotation around the C=C double bond.
(b) There are two different groups/atoms attached both ends of the double bond
Cahn–Ingold–Prelog (CIP) priority rules
- Compare the atomic number of the atoms directly attached to each side of the double bond; the atom of higher atomic number is given priority
- If the atoms are the same, consider the atoms at distance 2 from the double bond. Make a list of each atom bonded to the one directly attached to the double bond. Arrange list in order of decreasing atomic number. Compare the lists atom by atom; at the earliest difference, the group containing the atom of higher atomic number is given priority
Priority Group:
The atom with the bigger atomic number is classed as the priority atom
Petroleum fraction
mixture of hydrocarbons with a similar chain length and boiling point range
Draw fractional destillation mechanism
Key points to learn
about fractional distillation
- Oil is pre-heated
- then passed into the column.
- The fractions condense at different heights
- The temperature of the column decreases upwards
- The separation depends on the boiling point.
- Boiling point depends on the size of molecules.
- The larger the molecule the larger the van der Waals forces
- Similar molecules (size, bp, mass) condense together
- Small molecules condense at the top at lower temperatures
- and big molecules condense at the bottom at higher temperatures
Vacuum distillation unit
- Heavy residues from the fractionating column are distilled again under a vacuum.
- Lowering the pressure over a liquid will lower its boiling point.
Fractional Distillation: In the laboratory
Cracking:
conversion of large hydrocarbons to smaller hydrocarbon molecules by breakage of C-C bonds
Economic reasons for cracking
- The petroleum fractions with shorter C chains (e.g. petrol and naphtha) are in more demand than larger fractions.
- To make use of excess larger hydrocarbons and to supply demand for shorter ones, longer hydrocarbons are cracked.
- The products of cracking are more valuable than the starting materials (e.g. ethene used to make poly(ethene), branched alkanes for motor fuels, etc.
There are two main types of cracking:
thermal and catalytic
Thermal Cracking
Catalytic Cracking
Fuel :
releases heat energy when burnt
Complete Combustion
In excess oxygen, alkanes will burn with complete combustion
The products of complete combustion are CO2 and H2O
C8H18(g) + 12.5 O2 (g) —– 8CO2 (g) + 9 H2O(l)
Incomplete Combustion
If there is a limited amount of oxygen then incomplete combustion occurs, producing CO (which is very toxic) and/or C (producing a sooty flame)
CH4 (g) + 3 /2 O2 (g) —-CO(g) + 2 H2O(l)
CH4 (g) + O2 (g)—– - C(s) + 2 H2O(l)
Incomplete combustion produces less energy per mole than complete combustion
Carbon (soot) can cause global dimming- reflection of the sun’s light
Pollution from Combustion
Nitrogen Oxides NOx
Catalytic converters
Global warming
Carbon dioxide (CO2 ), methane (CH4 ) and water vapour (H2O) are all greenhouse gases.
Water is the main greenhouse gas (but is natural), followed by carbon dioxide and methane
Mechanism of the greenhouse effect
UV wavelength radiation passes through the atmosphere to the Earth’s surface and heats up Earth’s surface.
The Earth radiates out infrared long-wavelength radiation.
The C=O Bonds in CO2 absorb infrared radiation so the IR radiation does not escape from the atmosphere.
This energy is transferred to other molecules in the atmosphere by collisions so the atmosphere is warmed
Carbon dioxide levels have risen significantly in recent years due to the increased burning of fossil fuels.
Carbon dioxide is a particularly effective greenhouse gas and its increase is thought to be largely responsible for global warming
The Earth is thought to be getting warmer, and many scientists believe it is due to increasing amounts of greenhouse gases in the atmosphere
The reaction of alkanes with bromine/chlorine in UV light
Overall Reaction
CH4 + Cl2 —-CH3Cl + HCl
Example: Write mechanism of Br2 and propane
Primary halogenoalkane
One carbon attached to the carbon atom adjoining the halogen
Secondary halogenoalkane
Two carbons attached to the carbon atom adjoining the halogen
Tertiary halogenoalkane
Three carbons attached to the carbon atom adjoining the halogen
Haloalkanes
Nucleophilic substitution reactions
Comparing the rate of hydrolysis reactions
Nucleophilic substitution with aqueous hydroxide ions
Alternative mechanism for tertiary halogenoalkanes
Nucleophilic substitution with cyanide ions
Naming Nitriles
Nucleophilic substitution with ammonia
Elimination reaction of halogenoalkanes
Elimination with alcoholic hydroxide ions
The structure of the halogenoalkane also has an effect on the degree to which substitution or elimination occurs in this reaction
Primary tends towards substitution
Tertiary tends towards elimination
Uses of Halogenoalkanes
Chloroalkanes and chlorofluoroalkanes can be used as solvents
Halogenoalkanes have also been used as refrigerants, pesticides and aerosol propellants CH3CCl3 was used as the solvent in dry cleaning Many of these uses have now been stopped due to the toxicity of halogenoalkanes and also their detrimental effect on the atmosphere
ozone
The naturally occurring ozone (O3 ) layer in the upper atmosphere is beneficial as it filters out much of the sun’s harmful UV radiation
Ozone in the lower atmosphere is a pollutant and contributes towards the formation of smog
Man-made chlorofluorocarbons (CFC’s) caused a hole to form in the ozone layer. Chlorine radicals are formed in the upper atmosphere when energy from ultra-violet radiation causes C–Cl bonds in chlorofluorocarbons (CFCs) to break
CF2Cl2 —- CF2Cl. + Cl.
Cl radicals + ozone depletion equation+ description
Alkenes
unsaturated hydrocarbons
Alkenes bonds
C=C double covalent bond consists of one sigma (σ) bond and one pi (π) bond
π bonds are exposed and have high electron density. They are therefore vulnerable to attack by species which ‘like’ electrons: these species are called electrophiles
Reaction of Bromine with Alkenes
Reaction of Hydrogen Bromide with Alkenes
Reaction of Sulfuric acid with Alkenes
Direct industrial hydration of alkenes to form alcohols
Testing for Alkenes with Bromine water
Bromine water decolourises in the presence of a double bond. This can be used as a test for the presence of an double bond in a molecule. It can be used quantitatively to show the presence of multiple double bonds in compounds like polyunsaturated oils
Poly(chloroethene)
draw + describe
Poly(chloroethene) is a polymer that is waterproof, an electrical insulator, and doesn’t react with acids
In its pure form, it is a rigid plastic due to the strong intermolecular bonding between polymer chains that prevents them from moving over each other.
In this un-plasticized form it is used to make uPVC window frame coverings and guttering.
If a plasticizer is added the intermolecular forces are weakened which allows the chains to move more easily, resulting in more flexibility in the polymer.
In this form, PVC is used to make insulation on electrical wires, and waterproof clothing
Bond angles in Alcohols
All the H-C-H bonds and C- C-O are 109.5o (tetrahedral shape), because there are 4 bonding pairs of electrons repelling to a position of minimum repulsion
The H-O- C bond is 104.5o (bent line shape), because there are 2 bonding pairs of electrons and 2 lone pairs repelling to a position of minimum repulsion. Lone pairs repel more than bonding pairs so the bond angle is reduced
Boiling point
The alcohols have relatively low volatility and high boiling points due to their ability to form hydrogen bond between alcohol molecules
Partial Oxidation of Primary Alcohols
Distillation of an alcohol
Full Oxidation of Primary Alcohols
Reflux
Oxidation of Secondary Alcohols
Tollens’ Reagent
Fehling’s solution
Reaction of Alcohols with Dehydrating agents
Forming ethanol
fermentation
Forming ethanol
From ethene
Acid catalysed addition mechanism for hydration of ethene
Ethanol as biofuel
A biofuel is a fuel produced from plants
Ethanol produced from fermentation is a biofuel. It can be argued that ethanol produced from this method is classed as carbon–neutral because any carbon dioxide given off when the biofuel is burnt would have been extracted from the air by photosynthesis when the plant grew. There would be no net CO2 emission into the atmosphere
Equations to show no net contribution to CO2
Identification of functional groups by test-tube reactions
Alkene
Functional group
Reagent
Result
Bromine water
Orange colour decolourises
Aldehyde
Reagent
Result
Fehling’s solution
Blue solution to red precipitate
Tollens’ reagent
Silver mirror formed
Carboxylic acid
Reagent
Result
Sodium carbonate
Effervescence of CO2 evolved
1 o 2 o alcohol and aldehyde
Reagent
Result
Sodium dichromate and sulfuric acid
Orange to green colour change
chloroalkane
Reagent
Result
Warm with silver nitrate
Slow formation of white precipitate of AgCl
Optical Isomerism
Type of a stereoisomerism
Optical isomerism occurs in carbon compounds with 4 different groups of atoms attached to carbon (called an asymmetric carbon
Two compounds that are optical isomers of each other are called enantiomers
A carbon atom that has four different groups attached is called a chiral
Non-superimposable images of each other
Rotate plane-polarized light
A mixture containing a 50/50 mixture of the two isomers (enantiomers) is described as being a racemate or racemic mixture.
Many naturally occurring molecules contain chiral C atoms but are usually found in nature as a pure enantiomer
Optical isomers have similar physical and chemical properties, but they rotate plane polarised light in different directions.
One enantiomer rotates it in one direction and the other enantiomer rotates it by the same amount in the opposite direction
A racemic mixture (a mixture of equal amounts of the two optical isomers) will not rotate plane-polarised light.
Chemical Reactions and Optical Isomers
Formation of a racemate
A racemate will be formed in a reaction mechanism when a reactant or intermediate has a trigonal planar group in the molecule is approached from both sides by an attacking species
Nucleophilic addition of HCN to aldehydes and ketones (unsymmetrical)
