Functional Groups Flashcards
Why are alkanes known as paraffins ?
- due to unreactivity
What state are alkanes ?
- CH4 to C4H10 are gases
- C5H12 to C17H36 are liquids
- C18H38 and above are solids
Why does bp of Alkanes increase as chain length increases ?
- More London forces
- more surface points of contact
what is an electrophile ?
- electron lover
- accepts a pair of electrons
what is a nucleophile ?
- donates a pair of electrons
what is the HOMO?
- highest occupied molecular orbital
- nucleophile has pair of e- in the HOMO
what is the LUMO ?
- low energy anti-bonding orbitals
- lowest unoccupied molecular orbitals
what does a curly arrow represent ?
- movement of a pair of electrons from a filled orbital into an empty one
What is the difference between SN1 and SN2 mechanisms ?
- SN1 - leaving group goes first , carbocation produced and then nucleophile attacks
- SN2 - nucleophile attacks same time as leaving group goes so no carbocation
what 3 things does rate of an Sn2 reaction depend on ?
- nucleophile
- carbon skeleton
- the leaving group
also temp + solvent
what 2 factors does rate of Sn1 reaction depend on ?
- carbon skeleton
- the leaving group
temp + solvent
what is the RDS (rate-determining step) in Sn1?
- formation of carbocation
How does structure of carbon skeleton affect Sn1 reaction ?
methyl + 1°= no cause unstable carbocation
2° = moderate, slower than 3°
3° = fastest very stable cation
How does structure of carbon skeleton affect Sn2 reaction ?
methyl + 1°= fastest due to low steric hindrance
2° = moderate some steric hindrance
3° = no, high steric hindrance
what is steric hinderance ?
- slowing down of a chemical reaction due to bulk of other groups
How does steric hinderance affect Sn1 reactions ?
- stabilises carbocation
how does steric hinderance affect Sn2 reactions ?
- low steric hinderance easy for nucleophile to attack
what is a racemic mixture and how does it form in Sn1 reactions ?
Racemic -contains equal amounts of 2 enantiomers.
- in sn1 - when a chiral carbon forms a carbocation , nucleophile can attack from both sides
what is a polar protic solvent ?
- can form H bonds
eg. water, alcohol
what is an aprotic solvent ?
- cannot form H bonds
does sn1 take place in protic or aprotic solvents ?
- protic because they stabilise carbocation
does sn2 take place in protic or aprotic solvents ?
- apotric
how is the stereochemistry inverted in Sn2 ?
- nucleophile attacks from backside , side oppsodie to the one where leaving group goes
Does the double bond in Alkenes act as a nucleophile or electrophile ?
- nucleophile
How does conversion of alkene isomers occur ?
- breaking of pi bond
- eg. cis to trans conversion
What are the 2 methods of preparing alkenes ?
- cracking
- elimination of halides/alcohols or
how does cracking produce alkenes ?
- long chain alkanes are cracked to form a alkene and smaller alkane
When does anti - markovinikov addition occur?
’ Presence of peroxides
What are alkynes?
- Contains triple c-c bonds - 2 pi and 1 sigma bond
What is a stereospecific reaction ?
- stereochemistry of reactant determines stereochemistry of product
what is a diastereoisomer ?
-non- mirror images
what is the bromonium ion and is it an electrophile or nucleophile ?
- Br+
- electrophile
What is the inductive effect ?
- electron withdrawing groups (electronegative ) pull e- towards themselves through sigma bond
- electron donating groups (alkyl) push e- density onto positively charged center
Why is tertiary carbocation more stable than primary ?
- greater number of alkyl groups
- more carbons = increased positive inductive effect
What conditions are needed for anti-markovnikovs rule ?
- peroxide
- hydrogen bromide
Difference between anti and normal markovnikovs?
- anti uses radicals not carbocations
- in anti- H attaches to C with fewer H’s
- wheras in normal it attaches to one with most H’s
stages of anti-markovnikov addition
- initiation - RO–O–R→2RO*
- propagation - RO+HBr→ROH+Br
Br* adds to the less substituted carbon of the alkene, creates a new alkyl radical on the more substituted carbon of the alkene.
termination = Br+Br→Br2
alkylradical+Br*→bromoalkane
conditions for hydrogenation of alkenes
- 150c
- Ni,pt,pd (palladium) catalyst
which hybridsation of carbon is more electronegative ?
sp>sp2>sp3
what does tautomerisation of alkynes form ?
alkyne —> enol —-> ketone
what is an enol ?
- alkene with an OH group
How are haloalkanes prepared ?
- radical substitution of alkanes
- halogenation of alcohols
- electrophilic addition of alkenes
What happens to acidity as alkyl group increases (positive inductive effect)?
- Acidity decreases as alkyl group increases
What effect does negative inductive effect have on acidity ?
- increased acidity
What are 3 methods of preparing alcohols ?
- hydration of alkenes
- reduction of aldehydes and ketones
- hydrolysis of haloalkanes
reduction of aldehydes and ketones ?
- reduced by NaBH4 or LiAlH4 - acts as H- source
- aldehydes reduced to 1° alcohol
- ketone reduced to 2° alcohol
what is an alkoxide ion and how is it formed ?
- deprotination of OH
- R−O-
how are esters formed ?
- carboxylic acid + alcohol —–> ester
- in presence of acid catalyst
oxidation of alcohols ?
- 1° alcohol –> aldehyde –> carboxyllic acid
- acidified potassium dichromate
- 2° alcohol - ketone
what is the role of alcohol dehydrogenase ?
- converts alcohol to aldehyde
what is the aldehyde dehydrogenase ?
- converts aldehyde to carboxyllic acid
what is the shape and hybridisation of phenol ?
- sp2
- planar
is phenol more acidic than alcohols ?
- yes because the phenoxide ion is stabilised by resonance
what is the role of the hormone epinephrine ?
- fight or flight response
what are primary, secondary, tertiary, amines ?
- primary - 2H
- secondary - H
- tertiary - no H’s
why are amine salts more soluble compared to amines ?
- amine salts are ionic
- eg. NH3+Cl-
Is a H bond in alcohol or amine stronger
- alcohol because O is more electronegative
What is a zwitterion ?
- formed from amino acids
- have a NH3+ group and COO- group
- have a pH of 7
how are nitriles formed ?
- Alkyl halide + NaCN
how are amides formed ?
- Carboxyllic acid + SOCl2 + NH3
how are amides formed from amines ?
- Acid chloride (RCOCl) +
1 or 2 Amine
how are sulfonamides made?
- Sulfonyl chloride (R-SO₂Cl) and 1 or 2 amine
