Figure Number: 10-00-00CO Title: Figure 10.5 Caption: Comparison of transition states for SN2 attack on an electrophilic reactant by iodide and by fluoride. Notes: Since iodide is larger and more polarizable than fluoride, the iodide transition state has more overlap (bonding) between the nucleophile and the carbon reaction site. In protic media, fluoride nucleophile is stabilized relative to the transition state by hydrogen bonding, increasing the activation energy for the fluoride reaction. Iodide does not hydrogen bond to protic solvents, so it is not stabilized by hydrogen bonding relative to its transition state. Furthermore, the iodide transition state is stabilized relative to the iodide ion reactant by increased bonding between iodide and carbon, lowering the activation energy for the iodide reaction. Consequently, iodide is a better nucleophile than fluoride in protic solvents.

Figure Number: 10-00-03UN Title: Survival Compounds Caption: Structures of organohalides made by red algae and sea hares to protect themselves from predators. Notes: These organohalides are toxic and foul-tasting.

Figure Number: 10-00-09T01 Title: Table 10.1 Relative Rates of Sn2 Reactions for Several Alkyl Bromides Caption: Relative rates of SN2 reactions for several alkyl bromides. Notes: Alkyl halides in which the carbon reaction center is sterically hindered (crowded) react more slowly in SN2 reactions.

Figure Number: 10-01a,b Title: Figure 10.1 Caption: MO pictures of the interaction between the HOMO of a nucleophile and the LUMO of an electrophile in a front side vs. a back side attack by the nucleophile. Notes: In Lewis acid–base reactions, electrons flow from the Lewis base to the Lewis acid. Since electrons flow from the HOMO of one species into the LUMO of the other initially, it is normally appropriate to overlap the HOMO of the Lewis base (nucleophile) with the LUMO of the Lewis acid (electrophile). When this is done for SN2 reactions, the overlap is more favorable in the back-side-attack transition state than it is in the front-side-attack transition state.

Figure Number: 10-02 Title: Figure 10.2 Caption: Potential maps of approach of hydroxide ion nucleophile to methyl, primary, secondary, and tertiary halides. Notes: Back side approach of the nucleophile to the carbon reaction center becomes progressively more difficult in this series, making SN2 reactions progressively slower.

Figure Number: 10-02-01UN Title: SN2 Reactivity Caption: Relative reactivities of alkyl halides in an SN2 reaction. Notes: Reactivity decreases as back side access to the carbon reaction site gets more difficult.

Figure Number: 10-03 Title: Figure 10.3 Caption: Reaction coordinate diagrams for the SN2 reaction of hydroxide nucleophile with methyl bromide and with a more sterically hindered alkyl bromide. Notes: The transition state for the reaction involving the hindered alkyl halide has lots of atom–atom repulsions due to steric crowding, and is thus less stable than the transition state for the methyl bromide reaction. Thus, the methyl bromide reaction has a lower activation energy, and it is faster.

Figure Number: 10-04 Title: Figure 10.4 Caption: Ball-and-stick models showing an SN2 reaction between hydroxide ion and methyl bromide. Notes: The transition state for this reaction has a trigonal-bipyramidal shape. The nucleophile and leaving group are 180 degrees apart (axial), and the other three groups attached to the carbon reaction site are in the same equatorial plane, 120 degrees apart.

Figure Number: 10-04-05UN Title: Halide Basicities Caption: Relative basicities of the halide ions. Notes: Larger anions are more stable (i.e., less basic) than smaller anions.

Figure Number: 10-04-06UN Title: Halide Leaving Group Ability Caption: Relative leaving abilities of the halide ions. Notes: Leaving ability parallels anion stability, and therefore runs opposite to basicity.

Figure Number: 10-04-07UN Title: SN2 Reactivities of Alkyl Halides Caption: Relative reactivities of alkyl halides in an SN2 reaction. Notes: Alkyl halides with better leaving groups react faster in an SN2 reaction.

Figure Number: 10-04-08UN Title: Acid Strengths Caption: Relative acid strengths of second-row binary acids. Notes: Binary acids with more electronegative central atoms form more stable (less basic) conjugate base anions, and are therefore stronger acids than binary acids with less electronegative central atoms.

Figure Number: 10-04-09UN Title: Base Strength and Nucleophilicity Caption: Relative base strengths and relative nucleophilicities. Notes: Nucleophilicity parallels base strength in protic solvents.

Figure Number: 10-05-01UN Title: Size, Basicity, and Nucleophilicity Caption: Relationship between size, basicity, and nucleophilicity of the halide anions in protic solvents. Notes: In protic solvents, sizes and nucleophilicities of the halide ions parallel one another and trend in the opposite direction from basicities.

Figure Number: 10-05-02UN Title: Ion–Dipole Interactions Caption: Ion–dipole interactions between water molecules and an anion. Notes: Ion–dipole interactions between water molecules and nucleophilic anions reduce the nucleophilicities of anions.

Figure Number: 10-05-03T02 Title: Table 10.2 Relative Nucleophilicity Toward CH3I in Methanol Caption: Relative nucleophilicities of various nucleophiles toward methyl iodide in methanol. Notes: Relative nucleophilicities in methanol are determined by a combination of basicities and polarizabilities.

Figure Number: 10-05-07UN Title: Nucleophile Steric Effects Caption: Ball-and-stick models of ethoxide ion and tert-butoxide ion. Notes: Sterically hindered nucleophiles are less nucleophilic than smaller nucleophiles.

Figure Number: 10-05-14UN Title: Synthesis Using SN2 Reactions Caption: Various types of organic compounds can be prepared using SN2 reactions. Notes: SN2 reactions can often be irreversible. In these cases, the reaction proceeds preferentially in whichever direction it needs to to consume a stronger nucleophile and produce a weaker nucleophile.

Figure Number: 10-05-23T04 Title: Table 10.4 Relative Rates Alkyl Bromides SN1 Reaction Caption: Notes:

Figure Number: 10-06 Title: Figure 10.6 Caption: Reaction coordinate diagram for an SN1 reaction. Notes: Since the reaction is first-order in electrophile concentration but zero-order in nucleophile concentration, the nucleophile enters the reaction sequence after the rate-determining step, so that its concentration does not affect the speed of the reaction. Thus, the first step, formation of the carbocation, is rate-determining.

Figure Number: 10-06-01UN Title: SN1 Reactivity Caption: Relative reactivities of alkyl halides in an SN1 reaction. Notes: The reverse reactivity order is seen for primary, secondary, and tertiary alkyl halides in SN1 reactions and SN2 reactions. SN1 reactivity is governed by intermediate carbocation stability (tertiary cations are most stable and primary cations are least stable).

Figure Number: 10-06-04UN Title: Leaving Group Influence on SN1 Reactivity Caption: Relative reactivities of alkyl halides in an SN1 reaction. Notes: Electrophiles with less basic (more stable) leaving groups will react faster by SN1 because the stability of the intermediate produced by the rate-determining step in the SN1 reaction is a function of both the carbocation stability and the leaving group stability.

Figure Number: 10-06-49UN Title: Solvation of Anions and Cations by Water Molecules Caption: Ion–dipole interactions between water molecules and cations and anions. Notes: Water moleules orient themselves in such a way that their positively charged hydrogen atoms point toward anions and their negatively charged oxygen atoms point toward cations.

Figure Number: 10-06-50T07 Title: Table 10.7 Benzene ring Caption: Dielectric constants of some common solvents. Notes: The higher the dielectric constant, the more polar the solvent. The more polar the solvent, the faster an SN1 reaction goes. Polar solvents stabilize charged transition states of SN1 reactions which resemble a carbocation/leaving group anion intermediate more than they stabilize neutral reactant electrophile molecules. This lowers the activation energy for SN1 reactions.

Figure Number: 10-07 Title: Figure 10.7 Caption: Reaction coordinate diagram for a reaction in which the charge on the reactants is greater or more localized than the charge on the transition state. Notes: An SN2 reaction using an anionic nucleophile fits this profile in which a charged (nucleophilic) reactant is used in the rate-determining step, and the transition state has less localized charge. Therefore, polar solvents slow down SN2 reactions.

Figure Number: 10-08 Title: Figure 10.8 Caption: Reaction coordinate diagram for a reaction in which the charge on the transition state is greater than or more localized than the charge on the reactants. Notes: An SN1 reaction fits this profile in which a charged (nucleophilic) reactant is not used until after the rate-determining step, whereas the transition state has more charge than the reactant (neutral) electrophile. Therefore, polar solvents speed up SN1 reactions.

Figure Number: 10-08-05P29Sol Title: Problem 29 Caption: Ka expressions for dissociation of a neutral acid and for dissociation of a cationic acid. Notes: Neutral acids generate ionic products, so Ka for neutral acids increases in polar solvents which stabilize ionic products more than neutral reactant. Cationic acids generate cationic hydronium ion product, so polar solvents will stabilize reactants and products of cationic acid-dissociation reactions more or less equally. Ka should not change as much with solvent polarity for cationic acids as it does for neutral acids.

Figure Number: Title: Table 10.5  Comparison of SN2 and SN1 Reactions Caption: Notes:

Figure Number: Title: Table 10.6  Summary of the Reactivity of Alkyl Halides in Nucleophilic Substitution Reactions Caption: Notes:

Figure Number: Title: Table 10.8  The Effect of the Polarity of the Solvent on the Rate Caption: Notes:

Figure Number: 10-00-09T01 Title: Table 10.1 Relative Rates of Sn2 Reactions for Several Alkyl Bromides Caption: Relative rates of SN2 reactions for several alkyl bromides. Notes: Alkyl halides in which the carbon reaction center is sterically hindered (crowded) react more slowly in SN2 reactions.

Figure Number: 10-05-03T02 Title: Table 10.2 Relative Nucleophilicity Toward CH3I in Methanol Caption: Relative nucleophilicities of various nucleophiles toward methyl iodide in methanol. Notes: Relative nucleophilicities in methanol are determined by a combination of basicities and polarizabilities.

Figure Number: 10-05-23T04 Title: Table 10.4 Relative Rates Alkyl Bromides SN1 Reaction Caption: Notes:

Figure Number: 10-06-50T07 Title: Table 10.7 Benzene ring Caption: Dielectric constants of some common solvents. Notes: The higher the dielectric constant, the more polar the solvent. The more polar the solvent, the faster an SN1 reaction goes. Polar solvents stabilize charged transition states of SN1 reactions which resemble a carbocation/leaving group anion intermediate more than they stabilize neutral reactant electrophile molecules. This lowers the activation energy for SN1 reactions.