electrophilic aromatic substitution

electrophilic aromatic substitution

rxn that allows introduction of many different functional groups onto an aromatic ring

Arene-H combined with an electrophile

electrophile replaces H on the ring

overall rate of EAS

second-order as aromatic component and the electrophile are first-order

rate-determining step (rds) in overall rxn

formation of cation (1 molecule of arene and electrophile react to give intermediate)

orientation of substituents on arene ring

ortho, meta, or para

very fast reaction done with

toluene (methyl group is a ring activator)

electron-donating substituents mentioned

alkyl (R), amido (NHC(=O)R), alkoxy (OR)

electron-donating substituents prefer

ortho- and/or para-substituted products

electron withdrawing groups

nitro (NO2) and acyl (RC=O)

electron withdrawing groups prefer 

meta-substituted products 

when G group (EDG) stabilizes positive charge on resonance structures through electron release

favors formation of ortho- and para-substituted products

electron withdrawing groups destabilize all contributing resonance structures

meta-substitution would be favored because the partial positive charge in alpha complex if further removed from location of the group

azo dyes prepared by reaction of

aromatic diazonium salts w/ aromatic compounds bearing activating groups such as amino and hydroxy

color of organic molecule

depends on energy gap between pi and pi* orbital

when energy absorbed

electron promoted from pi to pi* orbital

direct dyes

water-soluble pigments; ionic, dipole-dipole, h-bonding interactions

disperse dyes

suspensions of insoluble pigments rather than aqueous solutions

vat dyes 

characteristically applied to fabric in soluble, reduced form of pigments and then chemically “fixed” through an oxidation process that converts the soluble pigment into an insoluble pigment

acidic dyes (such as having sulfionic acid group)

form salts w/ fabric molecules containing basic functional groups such as amino group

azo dyes consdiered

direct dyes, so functional groups on both the pigment and the fabric dictate how well the dye is retained

rayon fibers

different cellulose fibers

viscose rayon

fairly similar to cotton

acetate rayon

some of free hydroxyl groups in the cellulose molecule converted into acetate esters 

wood and silk

primarily strands of protein

wool

wide range of amino acids (lysine and glutamic acid) in primary structure; and alpha-helical secondary structure

silk

made of fibroin protein - specific repeating sequence of glycine-serine-glycine-alanine-glycine-alanine w/ beta sheet secondary structure

nylon

synthetic polyamide fiber formed by reacting diacid w/ diamine

combinatorial chemistry

common strategy for rapidly producing collection of molecules (compound library) that differ from each other in nature, position, and orientation of substituents

parallel synthesis

in which each compound is prepared individually, and activity is assayed separately for each compound

split synthesis

compounds are prepared as mixtures, and activity of mixture is evaluated; requires deconvolution

deconvolution

figuring out which compound is active when the mixture is tested