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chem 104 Lecture 3
substituent effects in benzene derivatives
33
Chemistry
Undergraduate 1
02/22/2013

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Term

in nomenclature 3 terms Ortho, Meta and Para are commonly used.

Now if a ring was 1,2 distributed what would its nomenclature be?

Definition
1,2 distribution is Ortho
Term
what nomenclature would 1,3 distribution have?
Definition
1,3 distribution is Meta
Term
when would you use Para nomenclature?
Definition
in a 1,4 distribution
Term
methylbenzene is also known as?
Definition
Toluene
Term
hydroxybenzene is also known as?
Definition
Phenol
Term
Methoxybenzene is also known as?
Definition
Anisole
Term
Aminobenzene or Phenylamine is also known as?
Definition
Aniline
Term
benzenecarboxylic acid is also known as?
Definition
benzoic acid
Term

nomenclature:

in di-or-multi substituted benzene derivatives, one of the common names (toluene, phenol) is used as a ROOT for the basis of the name.

prefixes used to name additional substituents with position relative to the root substituent always on C1 indicated by use of terms ortho, meta and para

Definition
ok.
Term
what group is C6H5 known as?
Definition
Phenyl Group
Term
in mono-substituted benzene rings who determines where the electrophile goes? is it the exisiting substituent or the incoming electrophile?
Definition
it is the existing substituent which directs the electrophile to ortho/para or to a meta position.
Term
name the 2 ways a substituent can affect benzene ring reactivity.
Definition

1. relative to the ring the substituent may be more or less  reactive toward further EAS

2. it controls which postion the incoming electrophile may attack directing it to ortho/para or meta postion

Term
what are the 2 types of substituents?
Definition
activating and deactivating substituents
Term
if toluene is nitrated 25 times faster then benzene under similar conditions what kind of substituent is toluene? (activating or deactivating)
Definition
it is an activating substituent
Term
an alkyl substituent (eg toluene) ............. the ring toward further EAS
Definition

activates

 

it speeds up and promotes EAS

Term
an alkyl substituent also directs incoming electrophiles to the ortho/para positions thus it is said to be a ......../......... ..............
Definition
ortho/para director
Term
given that a -COOH or -COOR substituent DEACTIVATES the ring towards EAS would benzoic acid be nitrated 200  times faster OR slower than benzene under normal conditions?
Definition

would be slower because -COOH is a deactivating substituent.

 

a -COOH or -COOR substituent also directs electrophile to the meta direction so is known as a meta director

Term
groups that activate the ring towards EAS are generally ortho/para directors. groups that deactivate the ring towards EAS are ?
Definition
meta directors
Term
name the four activating substituent groups
Definition

Amino -NH2

Alcoxy -OR

Alkyl -R

Hydroxy -OH

Term
name the 7 deactivating substituents
Definition

nitro -NO2

sulphonic acid -SO3H

nitrile -CN

ester -COOR

acid -COOH

Acyl -COR

Formyl -CHO

Term
why do halogens break the activating/deactivating substituents pattern?
Definition
they are weakly deactivating but are ortho/para directing
Term
what is the result of -OH and -NH2 groups being such highly activating substituents?
Definition
EAS reactions on phenol and aniline occur occur under mild conditions resulting in multiple ortho/para substitutions
Term
rings with strongly .............. substituents require much harsher condtions to undergo EAS reactions
Definition

deactivating.

 

eg. halogenation of nitrobenzene requires Br2/FeBr3 and strong heat at 140 C

Term

which of the following is deactivating and meta directing?

 

NO2, NH2, OH

Definition

NO2.

 

the other two are ortho/para directing and activating groups

Term
which two reactions cannot occur with deactivating substituents?
Definition
Friedel-Craft Acylation and Friedel-Craft Alkylation do not occur with deactivating substituents.
Term
a substituent may be electron donating or electron withdrawing but what affect (inducive or resonance) causes which?
Definition

electron withdrawing - caused by inducive effects

electron donating - caused by resonance effects

Term

atoms of high electronegativity eg, N, O and X (halogen) will .... electron density ....... of the ring by ............

 

 

Their inducive effect is electron-withdrawing

Definition

pull

out

induction

Term
a substituent only exerts resonance effects if the atom directly bound to the ring has what? (2)
Definition

1. one or more lone pairs on it

2. is involved in pi bonding to an O or N atom.

Term

a substituent can have resonance if it is directly attatched to the ring;

  • has one or more lp's
  • if it is involved in pi bonding with an O or an N atom. But which of the situations above would result in an electron donating substituent?
Definition

if it has one lone pair or more the resonance effects will be electron donating.

 

 

if the atom bound to the ring is involved in pi bonding with O or an N atom, the resonance effects will be electron withdrawing

Term
in halobenzenes, which effect is greater? the inductive or the resonance effect? what is the consequence of this?
Definition
the inductive effect is greater thus the consequence is that the ring is deactivated
Term
the positive charge of the arenium carbocation is delocalised over 3 carbons but in what direction relative to the  incoming elctrophile are they spread?
Definition
ortho and para to the postion of the incoming electrophile
Term

true or false?

resonance forms with the positive charge on C1 will have extra stability (lower energy) when G is electron-donating

Definition

true.

electron donating group stabilises the intermediates for ortho and para substitution more than for meta.

 

if the incoming electrophile goes ortho or para to the substituent group then the arenium ion intermediate has substantial +ve charge on the C1

Term
when substituent group is electron donating the intermediates for ortho and para substitution are .......... stable than for meta
Definition

more

 

 

 

so ortho and para products form faster (lower Ea) and dominate yield

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