Organic chem CAQ

☄ Organic chemistry Created Tags Questions regarding free radical substitution Why does it occur at high temperature? Sufficient energy for the X2 molecule to undergo homolytic fission to form free radicals Why is an atom like oxygen described as a free radical Write configuration of atom and identify unpaired electrons Identify the orbital the unpaired electrons is in Concept: radicals have unpaired electrons What is a free radical? An atom with an unpaired electron Explaining basicity of a compound Factor Explanation Delocalisation of electrons due to continuous overlapping of at least 3 adjacent p orbitals (usually amide) Delocalisation of lone pair of electrons to adjacent p orbitals due to presence of highly electronegative atoms , not available to accept H/donate lone pair of electrons to Sept ember 9 , 2025 125 AM Or ganic chemistr y 1

Factor Explanation accept H (only for Lewis bases or when in gaseous state due to absence of H , compound neutral (amide) Delocalisation of lone pair of electrons into benzene ring Less significant than delocalisation of p orbitals, decreased electron density, less likely for lone pair of electrons available to donate to accept H and donate pair of electrons in gaseous state or Lewis bases Presence of electron donating groups/ electron withdrawing EDGs intensify the electron density on atom causing the atom to be electron rich, lone pair of electrons more likely to donate to accept H EWG decreases electron density on atom, more likely to accept H Questions regarding major products formed in mechanisms Mechanism Explanation Free-radical substitution Expected product: count the number of hydrogen atoms actual product: Compounds that form tertiary radical will be formed in a greater proportion than expected as it is more stable due to the 3 electron donating groups, reducing electron defiency in order to stabalise the carbon radical for the intermediate of the compound followed by secondary and followed by primary (you can draw the radical intermediate) Answering structure: 1. State if itʼs primary, secondary or Or ganic chemistr y 2

Mechanism Explanation tertiary radical 2. State how many alkyl groups are there 3. More Electron donating alkyl groups help to reduce electron defiency making radical more stable Electrophilic addition/ SN2 Nu sub During the electrophilic addition/Nu sun mechanism, tertiary carbocation is the most stable as it consists of 3 electron donating alkyl groups to reduce electron deficiency of carbocation, stabalising it, followed by secondary carbocation and primary carbocation (you can draw the carbocation intermediates) Question regarding Nucleophillic substitutions Why certain molecules undergo SN1 rather than SN2 Conditions that favour SN1 Stable carbocation either by tertiary or resonance stabalised High steric hindrance due to bulky hydrocarbon groups attached to nucleophile, unable to do rear side attack Why certain compound unable to go through SN1 mechanism Will form carbocation that is not connected to any electron donating alkyl group but instead a EWG, intensifying positive charge on C making it unstable Which mechanism produces single enantiomer or racemic mixture Or ganic chemistr y 3

Sn2 mechanism occurs via rear side attack where nucleophile attack electron deficient carbon from opposite side of leaving group, producing a single enantiomer with an inverse stereochemistry SN1 can attack on both sides of the plane of the electron deficient carbon in a 5050 ratio, forming equal concentrations of each enantiomer producing a racemic mixture Explaining acidity of a compound Factor Explanation Presence of electron withdrawing groups/ electron donating groups Disperses negative charge of conjugate base, stabalise to a greater extent, dissociate into conjugate base and H more readily, more acidic EDG intensify negative charge on conjugate base, decrease stability and hence less likely to dissociate into H ,Milesʼs acidic Delocalisation into benzene ring Negative charge disperse, more stable , more acidic Questions regarding electrophilic substitution Why is Iodobenzene made in preference to chlorobenzene during reaction? Approach: explain in terms of electronegativity of the atoms, which atoms forms a more stronger electrophile Cl more electronegative than iodine ICl reacts with AlCl3 to form Iodine electrophile that reacts with electrons rich benzene to produce iodobenzene Or ganic chemistr y 4

Roles of the Lewis acid catalyst Act as a Lewis acid acceptor when reacting with reactants Acts as a catalyst as it is regenerated at the end of the reaction Why are products that have certain position of substituents Less likely to be formed? see if the group already there is 2,4 or 3,6 directing, Hence it will form a less stable intermediate and hence the formation of that product is unfavourable If there is an alkyl group, it can cause steric hindrance while electrophile is attacking at that position How Reactivity of benzene is affected certain substitutients on benzene ring with electrophile Presence of EDG, increase electron density of pi electron cloud of benzene ring, more susceptible to electrophillic substitution as compared to benzene as it is able to attract the electrophile more Presence of EWG decreases electron density of pi electron cloud making it less susceptible to electrophillic substitution Acidic hydrolysis of nitrile group HOCH2CN  H  2H2O ⎯  HOCH2COOH  NH4 Note: It is easier to balance using ionic equation as the SO42 ion is a spectator ion in the Acid hydrolysis Identifying major species in pH solutions Apply rule pH<pKa, species protonated Reasoning: at low pH, no need to give up H, can keep H Take note that NH3 is the default not NH2 Or ganic chemistr y 5

pH>pKa , species deprotonated At high pH, less H, need to give it up Why is LiAlH4 a stronger reducing agent than NaBH4 LiAlH4 is a stronger reducing agent than NaBH4 as the AlH bond is longer and weaker than BH bond Why does LiAlH4 not react with alkenes it uses H nucleophile for reduction and is usually attracted to partial charge of carbon like in carboxylic acid However it is repelled by electron rich CC in alkenes and hence reduction does not occur Reactivity with cold water Why does chlorobenzene not react with cold water C atom of of CCl is electron rich due to delocalisation pi electrons of benzene, repealing Nucleophillic H2O Partial double bond character CCl bond due to overlapping of the p orbital of cl with the pi electron cloud of benzene ring, much larger amount of energy is required to break the CCl bond Note: benzene ring is electron rich due to delocalisation and also has partial double bond character Why does ethanoyl chloride react with cold water? Presence of highly electronegative O atom and Cl atom attached to the carboxyl C atom makes the C atom highly electron deficient hence react rapidly with cold water Note: Need to know the concept that highly electron rich species repel nucelophiles Arene and alkenes) and highly electron deficient attract Nucleophille ( carbonyl) Or ganic chemistr y 6

Chloroethane does not react with water due to no electronegativite differences? Why does benzene only undergo substitution reactions but not addition reactions The ring of delocalised pi electrons gives benzene additional aromatic stability. Addition reactions destroy the aromaticity amd hence it is no favourable Hence it undergoes substitution reactions to preserve aromaticity Suggest how delocalisation of electrons occur with a diagram Continous side way overlap of p orbitals on 3 connected atoms allows pi electrons to delocalisation across these 3 atoms for diagram just show p orbitals How to know which resonance structure is most closely resembles structure of actual ion See where the lone pair electron lies If it lies on a more electronegative atom, delocalised electrons have a greater tendency t