Chem110 cheat sheet for mid semester one test PDF

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Summary

Carbon-carbon bond strength = conundrum Sigma bonds are stronger than pi bonds Single bond = 1 sigma bond Double bond = 1 sigma + 1 pi Triple bond = 1 sigma + 2 pi why double bonds are reactive but single bonds aren’t Hybridisation: 1s + 3p = 4sp³ , 4 identical orbitals = 4 sigma bonds Four atoms = ...

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Carbon-carbon bond strength = conundrum Sigma bonds are stronger than pi bonds Single bond = 1 sigma bond Double bond = 1 sigma + 1 pi Triple bond = 1 sigma + 2 pi - why double bonds are reactive but single bonds aren’t Hybridisation: 1s + 3p = 4sp³, 4 identical orbitals = 4 sigma bonds Four atoms = sp³, three atoms = sp², two atoms = sp Isomers: constitutional = different sequence of bonds, stereoisomers = different arrangement of groups, conformational = differ by rotation about a single bond, enantiomers = non superimposable mirror images, diastereomers = not mirror images Out of sync = staggered Bonds lineup = eclipsed Staggered is more stable Anti = larger groups furthest apart Gauche = larger groups close together Syn (least stable) = larger groups closest together H = equatorial hydrogen (more of these make the conformer more stable) H = axial hydrogens

E/Z isomers = cis/trans E = opposite sides Z = same side Prelog rules (CIP) rules: (hi/lo) each sp² hybridised carbon determines the relative priority Increasing priority = increased atomic number H < C < N < O < F < Cl < Br < I Enantiomers differ in their interaction with a chiral carbon medium or chiral reagent eg. plane polarised light. - compound is said to be optically active - one rotates clockwise (+), the other anticlockwise (-) A mixture of equal amounts of the two enantiomers is called a racemic mixture - gives an overall reaction of zero Determining absolute stereochemistry: (R/S) 1. The four groups attached to the C* are ranked from highest to lowest using CIP rules 2. Orient the molecule so that the lowest priority group (4) is pointing away from you

Contributing to boiling point = molecular size, shape, presence of polar bonds More polar = more water soluble (hydrophilic) Less polar = more lipid soluble (lipophilic)

Breaking covalent bonds: Symmetrically = homolytic bond cleavage Unsymmetrically = heterolytic bond cleavage

Homolytic: The species generated are called radicals, they are a neutral species with an unpaired electron. Heterolytic: electrons will move towards the more EN atom in the bond (which will become negative) Electrophile = positive, looking for electrons eg. HBr Nucleophile = negative, donate electrons eg. CH2=CH2 Substitution: break sigma bond, form pi bond Addition: break 1 pi bond, form 2 pi bonds Elimination: break 2 pi bonds, form 1 pi bond The detailed pathway by which a reaction takes place is known as the reaction mechanisms. - often requires multiple steps (elementary reactions) that occur sequentially. Nucleophilic substitution: Sn1 + Sn2 Reaction will involve breaking and forming sigma bonds, reaction will be nucleophilic. Sn1 = occurs stepwise, bond breaking then forming. heterolytic bond breaking to form carbocation intermediate, bond forming with H2O as the nucleophile, bond cleavage to give neutral product. Sn2 = bond breaking and forming occurs simultaneously (single step). Spectroscopy: Conjugation = pi - sigma - pi UV-VIS: radiation raises electrons in some molecules (generally those with pi bonds) from lower energy bonding (or non bonding) MOs to higher energy antibonding MOs. (molecular orbital) UV Spec: compounds containing only sigma bonds are generally transparent to UV-VIS light. σ -> π -> σ* -> π* (increasing energy) Energy and wavelength are inversely proportional - Any molecule containing conjugated double bonds will show absorption >200nm Beer's Law = Io (incident light), I (transmitted light) NMR is measured in delta, units ppm Change in energy for nuclear spin flip will depend on the shielding of the nucleus. Shielded = closer to zero 0-90 = sp3, single bonds 120-220 = sp2, double bonds Substituents containing double bonds will deshield. Vicinal = neighbouring

[R] = concentration of reactant [R]o = initial concentration of reactant e = exponential function k = rate t = time (s) ln = natural log Saytzeff rule: the major product is the most substituted alkene; the alkene with the least number o hydrogens directly attached to the carbons of C=C - alkenes are electron rich, they generally undergo addition reactions. Hydrogenation = reduction Markovnikov's Rule: addition of an unsymmetrical reagent to an unsymmetrical alkene, gives as the major product the compound in which the electropositive part of the reagent (usually H+) has bonded to the carbon of the C=C that is directly bonded to the greater number of hydrogen atoms. Lindlar's catalyst: It is used for the hydrogenation of alkynes to alkenes. Cis = lindlars catalyst Trans = Li/NH2 or H2O Addition of water - reagent = aq H2SO4/HgSO4 - for all alykes (except ethyne) the product is a ketone Reactions of aromatic compounds: - alkenes undergo addition reactions - benzene and substituted benzene usually undergo substitution reactions. - aromatic compounds like benzene have the extra stability of ‘resonance energy’ which essentially ‘prevents’ aromatic compounds from doing additional reaction chemistry. Disubstituted benzene = A controls the position of the incoming electrophile....