Alkanes Flashcards
Primary hydrogen
H atom bonded to a C atom that is bonded to 1 other C atom
Secondary hydrogen
H atom bonded to a C atom that is bonded to 2 other C atoms
Tertiary hydrogen
H atom bonded to a C atom that is bonded to 3 other C atoms
Why are alkanes non polar
Little difference in electronegativity between C and H, so C-H bonds are non polar
Why are alkanes generally unreactive
- Non polar; no electron rich sites to attract electrophiles and no electron deficient sites to attract nucleophiles
2; contains strong c-c and c-h bonds that require large amounts of energy to break
How is noiling and melting point affected in alkanes
Number of carbon atoms in alkanes imcrease, number of electrons imcrease, size of electron cloud ijcreases, easier to polarise electron cloud, strength of id-id increases, more energy needed to overcome
How does degree of branching affect melting and boiling point of alkane
The more branched the isomee of the alkane, molecule becomes more compact, more surface area available for intermolecular interactions, weaker id-id, less energy needed to overcome
Solubility of alkanes
Soluble in non polar solvents
Insoluble in water/highly polarnsolvents
How does size of alkane affect density
Density of alkanes increases with increasing molecular size of alkanes
Reduction of alkanes (page 7)
Alkene reacts with hydrogen under heat and with nickel catalyst to form alkane
Alkene reacts with hydrogen with Pt or Pd catalyst to form alkane
Combustion of alkanes
CnH2n+2 + (3n+1)O2 = nCO2 + (n+1)H2O
Complete combustion: CO2 and H2O produced
Incomplete combustion: CO, C as soot formed in additioj to CO2 and H2O
Describe halogenation
Reagent; Cl2 or Br2
Condiiton; uv light/heat
Mechanism; free radical subsitution
Halogenation with limited Br2
C2H6 (limting Br2, heat) = C2H5Br + HBr
Halogenation with excess Br2
C2H6 (excess Br2, heat) = C2Br6 + HBr
Characteristics of tree radical
- is highly reactive because it has a electron deficient site
- Is electrically neutralas it has equal number of protons and elections
How are radicals made stable
The more alkyl groups attached to carbon radical, the more stable the alkyl radical as alkyl groups are electron donatinf and make the radical less electron deficient
Define homolytic fission
Bond breaks in such way that each of the atok involved in forming the bond acquires 1 of the 2 bonding electrons to form 2 free radicals
Why is light only shone at the beginning of the subsitution reaction
Provides enough energy for some halogen moleculesto undergo homolyticbond fission to form radicals during initiation step
Chain reaction can step and propagation steps can proceed successively for manycycles unaided
What is a trace quantity
Compound that wasn’t formed in a propagation step
Contains at least twice the number of C atoms compared to starting alkane
Not the major product
How does stability of radical intermediate affect ratio of products formed
More stable radical intermediate and its subsequent is likely to beformed
How does type of hydrogenatoms affect ratio of products formed
Subsitution favours hydrogem attached to carbons that lead to more stable radicals
