aromatic chem Flashcards
aromatic means …
refers to molecules that contain 1 or more benzene ring. (i.e ring with conjugated pie systems).
what are benzenes useful in?
pesticides, polymers, dyes, painkillers like aspriin, paracetamol,ibruprofein. these all contain pie benzene rings.
conjugated pie systems arise from what?
alternating single and double bonds in which the electrons are delocalised.
give 3 examples of aromatic compounds, including benzene.?
ARENE - benzene attached with aryl/ alkyl group (methyl, ethyl, propyl etc) ITS FUNCTIONAL GROUP IS THE BENZENE RING ITSELF - eg: propylbenzene.
CHLOROBENZENE - BENZENE WITH CHLORINE AND CAN HAVE ARYL GROUPS ATTACHEDTO IT.ITS FUNCTIONAL GROUP IS THE BENZENE RING ATTACHED WITH THE CHLORINE (CHLORO BENZENE) EG 2-METHYLCHLOROBENZENE
PHENOL - FUNCTIONAL GROUP IS BENZENE RING ATTACHED WITH OH GROUP. CAN HAVE METHYL/ARLYGROUPS- EG, 2,3-DIMETHYLPHENOL.
WHY DOES BENZENE HAVE A PLANAR STRUCUTRE?
DUE TO THE HYBDRIDISATION OF SP^2 CARBON ATOMS AND THE CONJUGATED PIE SYSTEM IN THE RING.
EACH CARBON ATOM FORMS 3 PIE BONDS USING SP^2 ORBITALS. HOW DOES A PIE SYSTEM FORM.
THE REMAINING P ORBITALS OVERLAP LATERALLY WITH P ORBITALS OF NEIGHBOURING CARBON ATOMS. THIS SIDEWAYS OVERLAP OF P ORBITALS, RESULTS IN ELECTRONS BEING DELOCALISED AND BEING ABLE TO SPREAD AND MOVE FREELY OVER THE ENTIRE RING CAUSING A PIE SYSTEM TO FORM.
WHAT DOES A PIE SYSTEM CONSIST OF?
2 RING SHAPED CLOUDS OF ELECTRON DENSITY.
IN RELATION TO THE C-C BONDS, WHAT DOES THE DELOCALISATION OF ELECTRONS IN THE BENZENE RING MEAN? AND HENCE WHAT IS THIS EVIDENCE FOR?
IT MEANS THAT ALL OF THE C-C BONDS IN THESE COMPOUNDS ARE IDENTICAL AND HAVE BOTH SINGLE AND DOUBLE BOND CHARACTER. (MEANING THEY ARE EQUAL LENGTHS).
THE BONDS ALL BEING THE SAME LENGTH IS EVIDENCE FOR THE DELOCALISED RING STRUCTURE OF BENZENE.
WHATS THE ELECTROPHILIC SUBSTITUTION IN BENZENES.
when 1 hydrogen in the benzene is replaced by the electrophile.
draw the mechanism for electrophilic addition of benzene and elaborate whats occuring in each step.
https://merchanttaylorsschools-my.sharepoint.com/:w:/g/personal/tofoma_merchanttaylors_com/EXVi0JSfCmBJufF_qiYNHqgBffNAotED7-8O3lCYGtVS_Q?e=PHKSFp
in the nitration of benzene to form nitrobenze + h20, how is the No2+ ion generated.
by reaction of conc nitric acid (hn03) with conc sulfuric acid (h2so4). the reaction mixture of hno3 and h2so4 is refluxed with the benzene at 25-60 degrees.
give the reaction to generate the no2+ electrophile ion?
h2so4 + hno3 —–> no2+ +hso4- +h20.
why is the delocalised pie system highly stable?
as it is a region of high electron density.
equation for reforming the catalyst h2so4 used in the nitration of benzene?
h+ + hso4- —–> h2so4.
WHY DO ARENES predominantly UNDERGO SUBSTITUTION REACTIONS, rather than addition reactions. and why?
the delocalisation of electrons (also aromatic stability) in arenes is the reason why arenes predominantly undergo sub reactions, rather than addition. this is because in sub reactions, aromaticity is restored (hence stability/delocalisation of its ring is restored), whereas in addition its not and in some cases completely lost (the stability).
why are arenes very stable?
due to the delocalisation of electrons across the delocalised pie ring system. this is due to the delocalised electrons being distibuted across the entirely of the ring and not just one end.
alkyl arenes what type of reactions in which positions, due to what?
alkyl arenes undergo halogenation reactions in the 2 or 4 positions, due to the electron donating alkyl groups, which activate these positions.
what reaction mechanism are friedel-crafts reactions?
electrophilic substitution reactions.
why are arenes unreactive?
due to the aromatic stabilisation in them.
why are friedel-craft reactions used?
they are used to sub a H atom in the benzene ring for an alkyl group. which is friedel-craft alkylation. or used to sub a H atom in the benzene ring for an acyl group. this is friedel-craft acylation.
like any other electrophilic sub reaction, friedel-crafts reaction involves 3 steps. what are they?
1.) generating the electrophile
2.) the electrophile attack on the benzene ring
3) restoring the aromacity of the benzene ring
IN ORDER TO ADD ONTO THE BENZENE RING, THE ELECTROPHILE MUST HAVE A VERY WHAT?
VERY STRONG POSITIVE CHARGE.
IN FRIEDEL-CRAFTS ACYLATION, ACYL GROUPS HAVE A POSITIVE CHARGE HOWEVER ITS NOT POSITIVE ENOUGH. SO WHAT CAN WE USE TO PRODUCE A STRONGER ELECTROPHILE? HENCE WHAT DO REACT WHAT WITH WHAT?
WE CAN USE A HALOGEN CARRIER TO ACT AS A CATALYST (EG ALCL3), WHICH WILL PRODUCE A MUCH STRONGER ELECTROPHILE WITH A STRONGER POSITIVE CHARGE. HENCE IN FRIEDEL-CRAFTS ACYLATION, WE HAVE TO REACT AN ACYL CHLORIDE WITH THE HALOGEN CARRIER (ALCL3) TO CREATE A STRONGLY POSITIVE ELECTROPHILE.
THE REACTION OF THE ELCTROPHILE WITH BENZENE TO MAKE A LESS STABLE PHENYLKETONE IS DONE UNDER….
REFLUX AND A DRY ETHER SOLVENT.
