Alkanes Flashcards
C1H4- C4H10 are :
C5H12- C16H34 are :
Longer chain compounds are ?
Gases
Liquids
Waxes and harder solids
Compounds consisting of Only carbon and hydrogen atoms follow what formula ?
CnH(2n+2)
Which has a higher boiling/ melting point? Straight chain or a branched isomer?
Straight chain
Nucleophile characteristics ?
Normally negatively charges Nucleus loving Attracted to positive charge Stronger the base, stronger the Nucleophile Act as electron donors
Order of nucleophiles in regards to strength ? (Basicity)
RO-, HO-, RCO2-, ROH, H2O
Solvent that is able to form hydrogen bonds
Protic solvent
In a Protic solvent, the ____ the atom , the better the Nucleophile.
Order of Nucleophile strength?
Larger
CN-, I-, RO-, HO-, Br-, Cl-, F-, H2O
In an aprotic solvent, the nucleophiles are naked and thus Nucleophiles are based solely on _______
Order of the halogens for this?
Basicity
Fl-, Cl-, Br-, I-,
The best leaving groups are _____ bases
Order of halogens for leaving groups ?
Weak
I, Br, Cl, F
Rate of the reaction is dependent on only one molecule, the _____. What is this called ?
Carbocations
Uni molecular nucleophilic substitution
Explain the sn1 mechanism
Rds: lg leaves, carbocation forms
Step 2: Nucleophile attacks carbocation
Sn1:
Substrate reactivity :
Leaving group:
Nucleophile:
Tertiary-> methyl
Cl Br I weak bases, OH if protonated
Any Nucleophile
Sn1: Solvent ? Reaction mechanism? Rate law? Stereochemistry?
Polar Protic
2 steps
1st order, r=k(substrate)
Chiral –> racemic mix
Sn2
Substrate reactivity ?
Leaving group ?
Nucleophile ?
Methyl –> tertiary
Cl Br I, weak bases
Strong charged Nucleophile
Sn2: Solvent ? Reaction mechanism ? Rate law? Stereochemistry ?
Polar aprotic
Concerted 1 step
R=k(substrate)(Nucleophile)
Inversion of S/R
2 reasons why polar Protic solvents work best for Sn1?
Solvated carbocation intermediate
Form h bonds with leaving group
The transition state of the Sn2 forms what ?
Trigonal bipyramidal transition state
Typical polar Protic solvents?
Polar aprotic?
Water, alcohol
Acetone, DMSO
3 steps for a free radical substitution mechanism?
Initiation: diatomic halogens are cleaved by UV or peroxide forming free radicals
Propagation: radicals produce other radicals continuing the reaction
Termination: two free radicals combine to form a stable molecule
Bromine radicals tend to attack __ Alkanes vs chlorine which ___
Tertiary( very selective )
Depends on the stability of the intermediate and on the number of hydrogens present ( more likely to replace primary hydrogens) and react indiscriminately
Combustion reactions form ?
CO2, water and heat
When a molecule is broken down by heat in the absence of oxygen
Pyrolysis or cracking
Function of pyrolysis ?
Reduces avg molecular weight of heavy oils and increases the production of more desirable volatile compounds
