Aromatic Hydrocarbons Flashcards
(34 cards)
BENZENE is the ______ aromatic compound
BENZENE has a _____ structure
simplest
hybrid (due to delocalized π e-)
structural features of benzenes (6)
1.) cyclic and conjugated (π e- are delocalized over entire ring)
2.) planar molecule
3.) hexagon
4.) all carbons are sp2 hybridized
5.) all bond angles are 120 degrees
6.) all c-c bond lengths are 139 pm
what other types of aromatic compounds are there?
compounds that resemble properties of benzene
are benzenes stable? why or why not?
(2 reasons)
YES
- due to delocalized π e-
- due to cannonical resonance structures
_____ is the rule for aromaticity
- 3 criterias (lahat need)
Huckel (4n + 2) Rule
- Planar cyclic structure
- has cyclic clouds of π e- above and below the ring
- has 2,6,10,14…. number of π e-
*formula for number of π e- is 4n+ 2
*wherein n must be a whole number
for an aromatic compounds to be planar, how many carbon atoms must it have?
must have 7 or below carbon atoms
8 and above = non-planar
NOMENCLATURE
- parent name: _____
- substituted name: _____
- 4 different rules for 4 different cases?
- benzene
- phenyl
- Monosubstituted
- based on common name
- based on SUBSTITUENT + BENZENE - Disubstituted
- follows:
*ortho (adjacent)
*meta (separated by 1 carbon atom)
*para (separated by 2 carbon atoms)
- follows basic IUPAC rules - Highly Substituted
- follows a prioritization list for parent name
- substituent IN parent name is automatically position 1
4, Arenes (benzene as substituent = phenyl)
- ALKYLBENZENES: alkane (parent)
- ALKENYLBENZENE: alkene (parent) & prio is double bond
- ALKYNYLBENZENE: alkyne (parent) & prio is triple bond
PALATANDAAN in nomenclature of arenes?
automatic substituent si benzene is may alkene or alkyne parent chain
NOMENCLATURE - MONOSUBSTITUED
- 11 common names
- toluene
- phenol
- aniline
- benzoic acid
- benzaldehyde
- acetophone
- anisole
- styrene
- benzenesulfonic acid
- benzonitrile
- cumene
NOMENCLATURE - HIGHLY SUBSTITUED
- prioritization list (7)
- carboxylic acid
- aldehyde
3, ketone - phenol
- amine
- ethers
- alkenes/alkynes
REACTIONS
- MAINLY what type of reactions do they undergo?
- 5 types of ^^
ELECTROPHILIC AROMATIC SUBSTITUTION
- Aromatic Nitration
- Aromatic Sulfonation
- Aromatic Hydrogenation
- Friedel-Crafts Alkylation
- Friedel-Crafts Acylation
why do BENZENES react with ONYL electrophilic aromatic substitution (EAS)?
electrophilic
- the 6 delocalized π e- make the benzene ring electron rich -> reacts with electrophiles
aromatic
- benzene is very stable and reactions that preserve the aromaticity are favoured
substitution
- the way to preserve aromaticity since it does not undergo bond break or formation (unlike “addition rxns”)
EAS - MECHANISMS
- 3 steps
- addition of electrophile to form carbocation (ARENIUM ION)
- carbocation forms (SIGMA COMPLEX) as it is resonance stabilized, not aromatic
- loss of a proton to re-form the aromatic ring
EAS - AROMATIC NITRATION
- reagents (2)?
- products (2)?
- which is the electrophile?
HNO3 -> H2SO4
- benzene with NO2 + H3O+
*+NO2 is electrophile
EAS - AROMATIC SULFONATION
- reagents (2)?
- products (1)?
- which is the electrophile?
SO3 -> H2SO4
- benzene with SO3H
*HSO3+ or SO3 is electrophile
EAS - AROMATIC HALOGENATION
- reagents (3)?
- products (2)?
- ____ catalyst makes ____ more electrophilic by _____ to give _____
X2 -> Fe or FeX3
X = Cl or Br
- benzene with X + HX
- FeX3
- X2
- polarization
- FeBr4-Br+
EAS - FRIEDEL-CRAFTS ALKYLATION
- reagents (2)?
- products (2)?
- which is the electrophile?
- ____ helps the _____ ____ to ____ in the same way as ____ catalysis in halogenation
- alkyl halide (R-X)
- AlCl3
- benzene with R group + HX
*R+ is the electrophile
- AlCl3
- alkyl halide
- ionize
- FeX3
EAS - FRIEDEL-CRAFTS ALKYLATION
- limitations (3)
- only alkyl halides are used
- not possible for aryl halides
- not possible for vinylic halides - danger of polysubstitution
- no reactions for benzene rings pre-substitued with electron-withdrawing groups (meta-directors)
EAS - FRIEDEL-CRAFTS ACYLATION
- reagents (2)?
- products (2)?
- which is the electrophile?
- acid halide (XCOR)
- AlCl3
- aromatic ketone + HX
- NO polysubstitution since ketone molecule makes benzene less reactive as opposed to friedel-crafts acylation
SUBSTITUTION EFFECT
- states what?
- based on what theory?
*theory states that the _____ in EAS depends upon the tendency of a _____ group to _____ or _____ electrons either by _____ or _____
a pre-substituent of a benzene has an effect on the reactivity of the ring on different rxns
THEORY OF REACTIVITY AND ORIENTATION
- reactivity
- substituent
- release
- withdraw
- resonance
- induction
3 classifications of substituents in EAS
- Activating Groups
- Deactivating Groups
- Halogens
SUBSTITUENTS - ACTIVATING GROUPS
- electron-releasing or withdrawing?
- 2 processes?
- makes the benzene ring more ____ and more _____ via EAS
- direction?
- electron-releasing
- donate electrons via:
1. resonance effects - occurs in groups with atoms that possess lone pairs
2. inductive effects - shifting of e- density in response to pull of nearby atoms
- ortho-para directors
SUBSTITUENTS - ACTIVATING GROUPS
- substituents under the ff:
- strongly activating (4)
- moderately activating (2)
- weakly activating (2)
1.
- OH
- NH2
- NHR
- NR2
2.
- OR
- NHCOR
- R
- Ar (or aromatic ring)
SUBSTITUENTS - DEACTIVATING GROUPS
- electron-releasing or withdrawing?
- 2 processes?
- makes the benzene ring more ____ via EAS
- direction?
- electron-withdrawing
- withdraw electrons from the ring via:
1. resonance effects - occurs in groups with atoms attached to electrophilic ring or positive formal charge
2. inductive effects - electrons from ring are pulled towards the substituent due to electronegativity
- unreactive or less reactive
- meta directors
