Chapter 13 Benzene and Its Derivatives PDF

Bettelheim / Brown / Campbell / Farrell / Torres Introduction to General, Organic, and Biochemistry 11e Chapter 13 Benzene and Its Derivatives William...

Bettelheim / Brown / Campbell / Farrell / Torres Introduction to General, Organic, and Biochemistry 11e Chapter 13 Benzene and Its Derivatives William H. Brown Beloit College www.cengage.com/chemistry/bettelheim 1 Bettelheim / Brown / Campbell / Farrell / Torres Introduction to General, Organic, and Biochemistry 11e Chapter 13 Benzene and Its Derivatives William H. Brown Beloit College www.cengage.com/chemistry/bettelheim 1  historic articulate Structures 1872 : Russia & Germany were trying Aromatic Compounds to sort out the chemistry of alkenes -developed technology to isolate alkieves in a the same with aromatic pune form , t compounds they were confused be the - chemistry of alteres was very different to the chemistry of aromatic compounds - confused what the Structure of Benzene was Benzne is cyclic molecule Cotta Aromatic compound: A hydrocarbon that contains one or a nightmare About G python pitting its tail > - kekule had - a was more benzene-like rings. benzene is the Simplest Cot6 aromatic compound Arene: A term used to describe aromatic compounds. Ar-: A symbol for an aromatic group derived by removing an -H from an arene. Kekulé structure for benzene (1872). Benzene is Cyclic( arrangement ring like structure - in where atoms are in a alternating and - single O molecular orbital theory : double bonds Spc = each carbon atom has bondedthings 3 sp2 orbitals out 1200 it each porbital has an electron in - Pi bonds sideways overlap of e- - ⑧ 3 double bonds O F -trigonal planar each is spa hybridized - in the same plane ! Conjugatedwrongsee - bond- S + single 2  Found naturally crude Oil - in Benzene Carbonate ion : COg Chemistricnae develop to see of methods snape the molecules in benzene Resonance structure for benzene (1930s) each carboha atom panar the bonding - has - Benzene is a resonance with delocalized electrons same The theory of resonance developed by Linus Pauling provided the first adequate description of the structure of benzene. molecule that cannot be According to the theory of resonance, certain just described by on structure molecules and ions are best described by writing two or more Lewis structures. The real molecule or ion is a Loading… resonance hybrid of these structures. Each individual Lewis structure is called a contributing structure. We show that the real molecule is a resonance hybrid of the two or more Lewis structures by using a double- headed arrow between them. 3  -very special structure any Important 6 Carbon : > - atoms Benzene , single Benzene I an ex of a molecule that is aromatic not on -jugation-double bondst - > z characteristics - molecules 1) Stable - - not very reactive , needs a catalyst /resonance stabilization energy more stable than one would expect - > Benzene is more stable than 36kcal/mo Here are two contributing structures for benzene; with e-in being Hydrocarbon : it bond 3 it C C Oncea was the be it - de localized over = is stronger aromaticity wrong wrong is shorter ↳ believed and : entire ring the 2 a Stable btw single creating Delocalization 3 1930s carbon carbon bond kekure Conjugation on - in cloud · bond equal the top double bonds with electron cloud equal creates lengths lengths are all distinct actual structure (true) lengths, ring shaped molecules L is both Spz hybridized showinghow trigonal planer - in same plane (flatt Now : all carbon-carbon - every carbon has a p orbital bonds - equal 2 are in m - need a component of the 2 length cloud ze on *Two regions of e-density the bottom - * have to be moved in porbitals , cannot move in space The resonance hybrid has some of the characteristics of each Lewis contributing structure. ** The length of a carbon-carbon bond in benzene, for example, is midway between that of a carbon-carbon single bond and a double bond. DA No distinct single or double bonds , rather a uniform of sometimes benzene or aromatic Bond intermediate btw single electron density lengths drawn - are molecules a re this way double bonds the electron X and L showinga , density is spread out evenly circle why? of benzene be of structure Delocalization provides unique stability - and equal bond lengths 4  wa ⑦ short method : in video Q - & 3 diff writing - resonance at once structure Electrophilic electrophile aromatic - likes e- density L substitution reactions when an electrophine attacks benzene , it disrupts the anomatic system formin an thethre , intermediate Known as the Sigma can. has a t charge complex or avenium ion forming , - overs carbons the Cond show decolizations breaks electron carboraon defficient bond diff. Sprou O I forms a nitrogen- carbon bond of lost one Carbon - eation a intermediate ~ if you flow them Stabilized by e-you stabilize 3 resonance structures transition state O releases ?? be Q proton his I happens the ability the 6 resonance energy - Stabilized by of 4 pi bonds of the benzene to feed from Stable entity deficient the electron is formed aromatic want carbuncation that are things -high energy - intermediate to get stay aromatic activation energy acas Strong - donate a proton - - sulfuric acid - Catalyst it Benzene nitric acid 8 forms double bond - ~ nitratebenzene reaction does not Without a , catalyst a occur. With it does reaction carbon cation is - exothermic alway s sp2 # ⑦ hybridized amobilizing the charge - PAHs produced ex engine diesel engines in complete · combustion of hybrid a coal fired power plants > - energy to do work - Incomplete combustion generates these as a byproduct - BAD - D Polynuclear Aromatic Hydrocarbon (PAH) - can promote cancer if inhaling overtime Sof the don't 8 billion have real A hydrocarbon that contains two or more benzene rings, with each pair of rings sharing two adjacent carbon atoms. Loading… Naphthalene Anthracene Phenanthrene Benzo[a]pyrene 5  then morestable active thedocubsite due to Reactions of Benzene the stability alkanes X of these molecules the way to measure - * reactivity of Benzene Stability is to combust unique reactivity of Benzene or Benzene derivatives needs a catalyst them - > the molecule * aromatic compounds have something on 36 kg per mole, lower energy By far the most characteristic reaction of aromatic , content than to conjugating dromolecule - these molecules are compounds is substitution at a ring carbon. - more stable - lower energy content This reaction is called aromatic substitution. ! Some groups that can be introduced directly on the ring are the halogens, the nitro (-NO2) group, and the sulfonic acid (-SO3H) group. Halogenation: Catast occurs a ifYou put very different than - O addition reactions O ① Electrophiles Cl and Br don't like hydrogen is an heact but with exchanged , a catalyst they do for react. They react in molecule a different pattern than an alture reaction in addition 6 Reactions of Benzene strongeraciderconnectiona substitution catalyst a #important in pharmaceutical Nitration: having an amino group an Nh G , group on a benzene nitric acid ring is very important starting material in order to make whole host of pharmaceutical compounds 40 % of an drugs by product classified as aromatic substituted nitrogen compounds A value of nitroarenes is that the nitro group can be reduced to a primary amino group. be a reductionadded domwitrust hydrogen can only O - O - ingredient Sunscreen-absorbs in UV light 7 Reactions of Benzene Sulfonation: sulfuric Acid with benzene - An application of sulfonation is in the preparation of synthetic detergents. benzene ring with hydrocarbon ring end non polar end polar - G s 8 Nomenclature When two substituents occur on a benzene ring, three isomers are possible; they may be located by: - every carbon in benzene has a Hydrogen numbering the atoms of the ring or 3 diff. ways : using the locators ortho (o), meta (m), and para (p). 9 Phenols The functional group of a phenol is a hydroxyl ( -OH) group bonded to a benzene ring. Name substituted phenols either as derivatives of phenol or by common names. 10  aromatic-cycle of high e-that Stabilize a compound , unlike alkenes - addition reaction matters - Phenols soluble aromatic substitution not to - Astructure chemical - affects properties difference than -very large take hydrogen off a a with an OH a carpoxylic acid us a prenol benzene and replace Most phenols are weak acids, with pKa values in order to draw - resonance structures, e- must more through approximately 10. P Orbitals , not just space They are insoluble in water but react with strong bases, such as NaOH and KOH to form water-soluble salts. ar much more acid than when an - benzene alcohols due to structure can you ↓ de protonate Base delocalize ↓ the charge- more stabilizing it & for Loading… is O the lower energy compound , its content alcono functiona a G 10 are prends more , 000 times less acid than alcohol acidic than alcohol ? -more likely to donate *lower pKa-stronger the acid. #" than L · acconois - - different than another be of location of double bond 11 Phenols -not alcohols diff chemical , have + physical properties T -mportant in things Some phenols found in nature. all over living - ↓ O catha triggers the aroma to theSpice t h y m e aroma - of Vanilla response to reduce an oil (causes the iching 12  under condition on Oxidation Chemistry happens incorperates : - it can happen in room oxygen - organic molecules react w i t h Phenols as Antioxidants temp, high temp to molecular oxygen and degrade and create indue or lighttoo , problems. Diesel fuel is stored all around the world. They tend to oxidize and degrade. it oxidizes solid : cannot be used - > - forms into a , have to filter it put new filters in every so often - , Autoxidation: A reaction that converts an R-H group to an reactivity R-O-O-H (hydroperoxide). changed a change properties ↓ phys them.. - > - more polar allelic next to carbon - CH a carbon bond double molecular or ambient temp new functional group *Bad organic compound - endothermic allelic R 00 H Vinylic -H · 0-0-R - - H ↑ v - H S H It t It + , - C It radical - = C CH3 I 1) allic > - Ye = ↳ isiorbital-> - spiCH2 If It es that are CH3 CH3 CH2 1 away from a carbon carbon * allylic C-H double bond are one of the weak bonds - nearest CHS. hydroperoxyl like to break the weak bond 13 Phenols as Antioxidants Autoxidation is a radical chain reaction: Radical: An atom of molecule with an unpaired electron. used to generate radical Chain initiation: Formation of a radical from a A nonradical compound. CH Sharing 2e-Energy to break bond gets painedtenpaired ⑧ bond - - Sigma electron O O Obonded -radical anothe T Sp3 carbo om * cells do not want - this be it is living reaction (no ectet) generating thing this in a bad be it does not have is need/wants an. octet an. It octet Can cause a mutation 14  Phenols as Antioxidants Chain propagation: Reaction of a radical to form a new Chain reaction radical. - fast reaction look at rate functions Very - Propagation step 1: = molecular unique generate rbon cratical to oxygen-Structureestable a unpaired e-free radical Problem : - -the product of Step two is the of step starting one - rapidly turn into this repeat themselves will can - dyer Propagation step 2: over an Collides not a good thing > - O for - looking atom a hydrogen allilick CH Very unique chemically - Stable -specific with what it interacts with Callylic (H) - be they are weak ex. Jet fuel carbon center - forms a hydroperoxy radical radical - will tumble around in solution until aa drogen it interacts with a 15  - Ol bond on a prenol is neaher than Phenols as Antioxidants an allylic CH - Oils have many allylic CIts will undergo autoxidation · Hydroperoxides: Are unstable. Under biological conditions, they degrade to short- chain aldehydes and carboxylic acids with unpleasant "rancid" smells. Similar formation of hydroperoxides in the low-density lipoproteins deposited on the walls of arteries leads to cardiovascular disease in humans. In addition, many effects of aging are thought to be the result of hydroperoxide formation and their subsequent degradation. 16 Phenols as Antioxidants - limit oxidation Vitamin E is a natural antioxidant. BHT and BHA are synthetic antioxidants. - added to food-will create rancid These compounds are radical scavengers. They form stable radicals and thus break the cycle of chain propagation steps; they prevent further formation of destructive hydroperoxides. 17 Chapter 13 Benzene and Its Derivatives End Chapter 13 18 Nomenclature For three or more substituents: If one of the substituents imparts a special name, name the molecule as a derivative of that parent. If none of the substituents imparts a special name, number the substituents to give the smallest set of numbers, and list them in alphabetical order before the ending "benzene". 19 Nomenclature The common names for these monosubstituted benzenes are also retained Phenyl group (C6H5- or Ph-): The substituent group derived by removal of an H from benzene. 20 Nomenclature Monosubstituted alkylbenzenes are named as derivatives of benzene; for example, ethylbenzene. The IUPAC system retains certain common names for several of the simpler monosubstituted alkylbenzenes. 21