Basic Concepts & Hydrocarbons Flashcards
What are structural isomers?
Compounds with the same molecular formula but different structural formulas
Eg. Different placement of functional group or alkyl chain, different functional groups(ketone/aldehyde)
What are stereoisomers?
Organic compounds with the same with the same molecular formula and structural formula but a different arrangement of atoms in space
Eg. Double bond will not allow atoms to rotate freely
What are the Cahn-Ingold-Prelog rules?
- locate the c-c double bond in the molecule and redraw to show substituents.
- Assign priority of each substituent based on it’s mr, substituent with the highest mr is given the highest priority.
- if the highest priority groups are on the same side of the c-c double bond the isomer is Z if they are on different sides then the isomer is E.
What is Cis-Trans isomerism?
A type of E/Z isomerism where two substituents on each carbon atom are the same.
E is a trans isomer and Z is a Cis isomer
What is homolytic fission?
When a covalent bond breaks and each electron goes to a different bonded atom. This generates two reactive neutral species called radicals
What are radicals?
Highly reactive, neutral species which have one or more unpaired electrons shown as dots
What is heterolytic fission?
When a covalent bond breaks and both electrons go to one of the bonded atoms this results in one anion and one cation
What is covalent bond formation?
When two radicals or oppositely charged ions collide
What are carbocations?
Very reactive, unstable intermediates
Explain bonding in alkanes
- Each covalent bond has direct overlap of the electron clouds from each atom making a sigma bond (C-H and C-C)
- every carbon atom has a tetrahedral shape; bond angle 109.5
Are alkane molecules polar? Why?
- they are non-polar
- carbon and hydrogen have a similar electro negativity
- London forces/induced dipole dipole forces are the intermolecular forces due to instantaneous charge distribution
How does chain length effect the boiling points of alkanes?
- Boiling point increases as molecules increase in size
- this is due to increased intermolecular forces due to larger surface contact between adjacent molecules of
How does branching effect boiling point?
- branched molecules can’t fit together as nearly
- fewer surface area interactions
- weaker intermolecular forces due to fewer London forces
What do alkanes have low reactivity?
- all the covalent bonds have high bond enthalpies
- C-H sigma bonds have low polarity
What does complete combustion of alkanes look like?
A blue flame will be produced
What will incomplete combustion of alkanes look like? And what is produced?
A dirty yellow flame is produced
Water, carbon dioxide and carbon monoxide (CO)
What are the 3 states of radical substitution?
- Initiation- formation of the radicals
- propagation- two repeated steps that build up the desired product in a side-reaction.
- termination-two radicals collide to make a stable product.
Explain the bonding in alkenes
Double covalent bond has two sections:
- two sigma bonds are formed by electron clouds of two carbon atoms overlapping
- pi bonds are formed by the electrons in adjacent p-orbitals overlapping above and below the carbon atoms(can only take place after a sigma bond is formed)
Which is weaker pi bond or sigma bond?
Pi bond is weaker
What are electrophiles?
Species that are electron pair acceptors
What is hydrogenation?
The addition of hydrogen across a c-c double bond
-hydrogen and alkene are mixed and passed over a nickel catalyst at a temp of 150 degrees c
What is halogenation?
Addition reaction when a halogen is added across a c-c double bond
Alkene becomes saturated producing a dihaloalkane
How can you test for an unsaturated compound?
When bromine solution or iodine solution is mixed with a saturated compound- no reaction
Unsaturated compound- decolorisation
What is hydration?
Addition reaction between a gaseous alkene and steam - used to make alcohols
-requires 300 degrees c phosphoric acid catalyst
How can you carry out the addition of hydrogen halides to an alkene?
Hydrogen halides are gases at room temperature, these reactants are bubbled through the alkene
-produces a haloalkane
What carbon will the halide bond with when a hydrogen halide is added to an unsymmetrical alkene?
When H-X is added to an unsymmetrical alkene the hydrogen becomes attached to the carbon with the most hydrogen atoms attached to it
How are polymers formed from alkenes?
The pi bond within the c-c double bond is broken and the electrons from the pi bond form sigma bonds with neighbouring molecules
How can you draw the structure of polymers?
Draw square brackets and add a subscript ‘n’
What is a homologous series?
Substances that share the same functional group with successive members differing by one CH2 unit
What are aliphatic hydrocarbons?
In which the carbon atoms are joined together in branched or unbranched chains
What are alicyclics hydrocarbons?
In which the carbon atoms are joined together in a ring structure but are not aromatic
What are aromatic hydrocarbons?
Where there is at least one benzene ring in the structure
