Alkanes Flashcards
What is the general formula of alkanes?
CnH2n+2
What is the shape around every carbon atom?
Tetrahedral
109 degrees
What are the 2 conformations of alkanes?
Eclipsed
Staggered
Which of the 2 conformations of alkanes are more stable?
Staggered as there is maximum separation
What are the 2 types of isomers?
Structural
Stereo/geometric
What are the 3 types of structural isomers?
Branched
Functional group
Branched
What are the 3 types of stereo isomers?
E/Z
Cis/Trans
Optical
Definition of structural isomers
Same molecular formula but different structural formula
What are branched isomers?
Branch it (same number of Cs)
What are functional group isomers?
Change functional group
Eg alcohol-ester
What are positional isomers?
Change position of functional group
What is heterolytic bond fission?
Makes positive and negative ions
Pair of electrons in covalent bond go to one of the atoms that is bonded
What does a curly arrow show?
Movement of a pair of electrons
What is homolytic bond fission?
Makes radicals
1 electron in pair of electrons goes to each atom in covalent bond
What are radicals?
Species with an unpaired electron that are very reactive
What do fish hooks/half arrows show?
The movement of 1 electron
What are the three types of reactions for alkanes?
Elimination
Substitution
Addition
What are the 2 types of covalent bond?
Sigma (single)
Pi (double)
What are stronger sigma or Pi bonds?
Sigma
Definition of sigma bonds
End on overlap of orbitals on the line directly between bonded atoms.
What forces are between alkanes?
LDF
What 2 things affect the boiling point of alkanes?
Number of electrons (mainly)
Surface area of contact (if same number of e-)
When comparing boiling points, what do you say if one has more electrons?
More electrons so larger instantaneous/ induced dipoles so stronger LDF so more energy needed to break forces so higher boiling point.
When comparing boiling points, what do you say if they have the same number of electrons but 1 is branched?
Same number of electrons however X does’t have branches so there is a larger surface area of contact so stronger LDF so more energy needed to break forces so higher boiling point.
How many alkanes are gases at room temperature?
The first 4
What is produced in complete combustion?
Carbon dioxide (g) and water (l)
What is produced in incomplete combustion (normally)
Carbon monoxide (g) and water (l)
What is produced in incomplete combustion (when a solid is produced)
Carbon (s) and water (l)
What is produced when an alkane reacts with a halogen?
Haloalkane + hydrogen halide
What is the mechanism called when an alkane reacts with a halogen?
Free radical substitution
What are the condition is needed in free radical substitution?
UV light
What are the 4 steps to a free radical substitution answer?
Overall equation
Initiation
Propagation
Termination
What happens in initiation (free radical substitution)
Radicals are made
Remember to say homolytic bond fission!
What happens in propagation step 1? (free radical substitution)
Organic+radical goes to (Organic-H radical) and hydrogen halide
What happens in propagation step 2? (free radical substitution)
(Organic-H radical)+halogen goes to haloalkane and radical
What happens in termination? (free radical substitution
Radicals combine
What is the first problem with free radical substitution?
Can get substitution at different positions
What is the seconds problem with free radical substitution?
Can get more substitutions than wanted
How do you limit more substitutions occurring in free radical substitution?
Have excess of the organic substance so radicals always react with that instead of products that are made in the reaction.
What is added in free radical when you want 2 Hs to be substituted?
2CL2/2Br2/2I2
2 halogen halides are also made
