module 4: core organic chemistry Flashcards
what are structural isomers?
compounds with the same molecular formula but different structural formulae
what is a hydrocarbon?
a compound that contains only hydrogen and carbon
what does saturated mean?
containing single bonds only
what does unsaturated mean?
containing a double carbon-carbon bond
what is a skeletal formula?
a simplified organic formula
what is a homologous series?
a series of organic compounds with the same functional group (similar chemical properties) whose successive members differ by the addition of a -CH2- group
what is the general formula for alkanes?
CnH2n+2
what are alkanes?
saturated hydrocarbons
what are alkenes?
unsaturated hydrocarbons
what is a functional group?
the part of the organic molecule responsible for its chemical reactions
what are the products of the complete combustion of alkanes?
carbon dioxide + water
what are the products of the incomplete combustion of alkanes?
carbon monoxide (or carbon) + water
describe the reactions of alkanes with halogens
- alkanes react with halogens, but only in the presence of sunlight
- high energy UV radiation present in sunlight provides the initial energy for a reaction to take place
what type of reaction is that of alkanes with halogens?
a substitution reaction - a hydrogen atom in the alkane is substituted by a halogen atom
what are the three stages that make up the mechanism of the bromination of alkanes?
step 1 = initiation
step 2 = propagation
step 3 = termination
describe what happens in the first stage of the bromination of alkanes
stage 1 = initiation
- the reaction is started when the covalent bond in a bromine molecule is broken down by homolytic fission
- each bromine atom takes one electron from the pair, forming two highly reactive bromine radicals
- energy for this bond fission is provided by UV radiation
Br - Br –> Br* + Br*
what is a radical?
a very reactive species with an unpaired electron
describe what happens in the second stage of the bromination of alkanes
stage 2 = propagation
- the reaction propagates through two propagation steps, a chain reaction
Propagation step 1: CH₄ + Br* –> ·CH3 + HBr
Propagation step 2: ·CH3 + Br2 –> CH3Br + Br*
what happens in the first propagation step?
a bromine radical reacts with a C - H bond in the methane, forming a methyl radical and a molecule of hydrogen bromide
what happens in the second propagation step?
each methyl radical reacts with another bromine molecule, forming bromomethane and a new bromine radical
describe what happens in the third stage of the bromination of alkanes
- two radicals collide, forming a molecule with all electrons paired
- there are a number of possibilities
- when two radicals collide and react, both radicals are removed from the reaction mixture, stopping the reaction
what can hydrocarbons be classified as?
- aliphatic
- aromatic
- alicyclic
what are aliphatic hydrocarbons?
carbon atoms are joined to each other in an unbranched (straight) or branched chains, or non-aromatic rings
what are alicyclic hydrocarbons?
carbon atoms are joined to each other in ring (cyclic) structures, with or without branches
what are aromatic hydrocarbons?
some or all of the carbon atoms are found in a benzene ring
what is homolytic fission?
the breaking of a covalent bond where each of the bonded atoms take one of the shared pair of electrons from the bond
what is heterolytic fission?
the breaking of a covalent bond where one of the bonded atoms takes both of the electrons from the bond
what are the two types of bond fission?
homolytic and heterolytic fission
in a reaction mechanism, what do curly arrows represent?
movement of electron pairs when bonds are being broken or made
what is a sigma bond?
the direct overlap of two orbitals
what is a pi bond?
the sideways overlap of two p-orbitals
explain the effect of increasing chain length on the boiling points of alkanes
- increased chain length
- greater surface area of contact
- stronger london forces
- more energy required to overcome these forces
- boiling point increases
explain the effect of branching on the boiling points of alkanes
- more branching
- less surface area of contact
- weaker london forces
- less energy required to overcome these forces
- boiling point decreases
what is a nucleophile?
an electron pair donor
what is an electrophile?
an electron pair acceptor
state and explain how the rates of hydrolysis of the chloroalkane and the bromoalkane would differ
- rate slower with the chloroalkane
- C-Cl bond is stronger than C-Br bond
what are the reagents and conditions for an alkene to alcohol reaction?
steam and acid catalyst
what are the reagents and conditions for an alkane to haloalkane?
halogen and UV
state what is meant by the term ionic bond
electrostatic attraction between positive and negative ions
describe the use of aqueous barium chloride in qualitative analysis
- test for sulfate ions
- white precipitate forms
describe the oxidation reactions of butan-1-ol forming an aldehyde and carboxylic acid
oxidation reaction forming an aldehyde:
- acidified potassium dichromate
- heat and distillation
- organic product is butanal
oxidation reaction forming a carboxylic acid:
- acidified potassium dichromate
- heat under reflux
- organic product is butanoic acid
suggest the general formula for a carboxylic acid
CnH2n+1COOH
what are the differences between pi and sigma bonds?
- a sigma bond is between bonding atoms and a pi bond is above and below the bonding atoms
- a sigma bond has direct overlap of orbitals and pi bond has sideways overlap of orbitals
- pi bond has a lower bond enthalpy
- sigma bond has electron density between bonding atoms and pi bond has electron density above and below bonding atoms
what are the reagents for an alcohol to haloalkane reaction?
sodium halide and sulfuric acid
what are the reagents for an alkene to haloalkane reaction?
hydrogen halide
what are the reagents for an alcohol to alkene reaction?
concentrated sulfuric acid
what are the reagents for an alkene to alkane reaction?
H₂ and nickel catalyst
