Ch 4: Analyzing Organic Reactions (5%)

acidic solutions

In what kind of solutions does water act as a base?

basic solutions

In what kind of solutions does water act as an acid?

strength of an acid in solution

What does the acid dissociation constant (Ka) measure?

Ka = [conjugate base] / [acid]

write out the formula for calculating the strength of an acid in solution

pKa = -log(Ka)

write out the formula for calculating pKa

small

Do you expect strong acids to have a SMALL or LARGE pKa?

large

Do you expect strong bases to have a SMALL or LARGE pKa?

increase

Does acidity INCREASE or DECREASE as you go down the periodic table?

acidity

As bond strength decreases down the periodic table, ________ increases

alcohols, aldehydes, ketones, carboxylic acids

Name the 4 main functional groups that act as acids

amines, amides

Name the 2 main functional groups that act as bases

negative charge (aka anions), lone electron pairs, pi bonds (double/triple bonds)

What do nucleophiles have that make them want to form new bonds to electrophiles? (3 → can have one or multiple of these)

bases

Do good nucleophiles tend to be good ACIDS or good BASES?

increase

For nucleophiles, as basicity increases, does reactivity INCREASE or DECREASE?

charge, electronegativity, steric hindrance, solvent

Name the 4 major factors that determine nucleophilicity

increase

Does nucleophilicity INCREASE or DECREASE with increasing electron density (more negative charge)?

decrease, the atoms are less likely to share electron density

Does nucleophilicity INCREASE or DECREASE with increasing electronegativity?

Why?

decrease

Does nucleophilicity INCREASE or DECREASE with increasing bulkiness/sterics?

contain OH or NH bonds (H bound to highly electronegative atoms)

Describe the features of polar protic solvents

lack OH or NH bonds

Describe the features of polar aprotic solvents

increase

In polar protic solvents, does nucleophilicity INCREASE or DECREASE down the periodic table?

decrease

In polar aprotic solvents, does nucleophilicity INCREASE or DECREASE down the periodic table?

I-, Br-, Cl-, F-

Rank the nucleophilicity of the following halogens in order from most to least nucleophilic when in protic solvents:

F-, Cl-, I-, Br-

F-, Cl-, Br-, I-

Rank the nucleophilicity of the following halogens in order from most to least nucleophilic when in aprotic solvents:

F-, Cl-, I-, Br-

aprotic solvents

In WHAT kind of solvents does nucleophilicity relate directly to basicity?

polar solvents, the polar reactants wouldn’t dissolve in nonpolar solvents

What kind of solvent is required to perform nucleophile-electrophile reactions?

Why?

strong

Are the following STRONG, FAIR, or WEAK nucleophiles?

HO-, RO-, CN-, N3-

fair

Are the following STRONG, FAIR, or WEAK nucleophiles?

NH3, RCO2-

weak

Are the following STRONG, FAIR, or WEAK nucleophiles?

H2O, ROH, RCOOH

amines

Which functional group tends to make good nucleophiles?

positive charge (either fully or partially)

What do electrophiles have that make them want to form bonds with nucleophiles? (1)

increase

Does electrophilicity INCREASE or DECREASE as positive charge increases?

increase, resonance stabilizes the conjugate base

Does acidity INCREASE or DECREASE with increasing resonance stabilization?

Why?

alcohols, aldehydes, ketones, carboxylic acids

Name the 4 functional groups that acts as electrophiles

its ability to stabilize the extra electrons

What about a leaving group makes it good or not?

weak, they are more stable with an extra set of electrons

Do STRONG or WEAK bases make good leaving groups?

Why?

good

Do the conjugate bases of strong acids (like I-, Br-, and Cl-) make GOOD or BAD leaving groups?

weak

Do strong acids have STRONG or WEAK conjugate bases?

weak

Do strong bases have STRONG or WEAK conjugate acids?

resonance, inductive effects from electron-withdrawing groups

name the 2 things that can increase a leaving group’s leaving ability (make it a better leaving group)

leaving group leaves and creates carbocation (rate-limiting step), nucleophile attacks carbocation

write out the general step(s) for an SN1 reaction

increase, the alkyl groups act as electron donors to stabilize the positive charge

As a carbocation gets more substituents in an SN1 reaction, does its stability INCREASE or DECREASE?

Why?

just the substrate

When calculating the rate of an SN1 reaction, does the rate depend on just the concentration of the substrate or the concentrations of both the substrate and nucleophile?

both

When calculating the rate of an SN2 reaction, does the rate depend on just the concentration of the substrate or the concentrations of both the substrate and nucleophile?

less

In nucleophilic substitution reactions, does the leaving group need to be MORE or LESS reactive than the nucleophile?

nucleophile performs a backside attack on the carbon at the same time that the leaving group leaves

write out the general step(s) for an SN2 reaction

it must be strong

What must be true about the nucleophile in an SN2 reaction for the reaction to proceed?

it cannot be sterically hindered

What must be true about the substrate in an SN2 reaction for the reaction to proceed?

increase

For SN1 reactions, does reactivity INCREASE or DECREASE as the substrate becomes more substituted?

decrease

For SN2 reactions, does reactivity INCREASE or DECREASE as the substrate becomes more substituted?

-4, each H has an oxidation state of +1

What is the oxidation state of CH4?

Why?

+4, each O has an oxidation state of -2

What is the oxidation state of CO2?

Why?

decrease the # of bonds to hydrogen (increasing the # of bonds to O, N, other C, or halides)

Describe what it means in practice for a compound to get oxidized

increase the # of bonds to hydrogen (decreasing the # of bonds to O, N, other C, or halides)

Describe what it means in practice for a compound to get reduced

metals bonded to lots of oxygen, unusually high oxidation states

Describe the features of good oxidizing agents (2)

metals bonded to lots of hydrogen

Describe the features of good reducing agents (1)

highest

Are nucleophilic reactions more likely to occur at the LOWEST or HIGHEST priority functional group?

highest

Are redox reactions more likely to occur at the LOWEST or HIGHEST priority functional group?

more, resonance stabilization of the enol form

Are alpha-hydrogens MORE or LESS acidic than a regular C-H hydrogen?

Why?

protecting groups can sterically hinder leaving groups from being reacted with temporarily

How can sterics come into play with leaving groups?