Organic Chemistry Exam 3 Terms

Alkyl Halide

A compound with a halogen connected to an sp3 carbon

Aryl halide

Aromatic compound where one or more hydrogen bonded to an aromatic ring is replaced by a halide ion (F, Cl, Br, I)

Vinyl halide

Compound with the presence of a CH2=CH bonded to a halogen atom (F, Cl, Br, I)

Substitution alkyl halide reaction

Nucleophile replaces the halogen

Elimination alkyl halide reaction

A pi bond is formed

Nucleophile

Attracted to a + charge while being a - charged species (“nucleus-loving”)

Electrophile

Attracted to a - charge while being a + charged species (“electron-loving”)

Leaving group

Group capable of separating from a compound

Good leaving groups

Are the conjugate base of an acid with a pKa of less than 0

SN2

Type of nucleophilic substitution reaction where a nucleophile displaces a leaving group from an alkyl halide in a single concerted step (fast!)

SN1

Type of nucleophilic substitution reaction where the rate-determining step involves the formation of a carbocation intermediate. Nucleophile displaces halogen atoms to an alkyl halide molecule forming a new product (slowww, stepwise))

Hammond postulate

Transition state will resemble the structure of the nearest stable species

Exergonic

Transition state looks more like the reactants (releases energy=heat, ΔG<0)

Endergonic

Transition state looks more like the products (takes energy from surroundings=cold, ΔG>0)

Peak

Represents a transition state

Valley

Represents an intermediate

Concerted mechanism

Reaction happens all at the same time

Kinetics of Sn2 Reaction

2nd order, Rate=K [alkyl halide][nucleophile]

What happens if the concentration of the nucleophile were doubled?

Reaction rate would double

Stereospecificity of Sn2

Always inverts the configuration

Where do nucleophiles attack?

From the back (side opposite of the leaving group)

What alkyl halide will an Sn2 reaction not occur and why?

Tertiary because there is no room for a backside attack to occur

How many transition states does Sn2 have?

1

How many intermediates does Sn2 have?

0

What type(s) of alkyl halide do Sn2 reactions require?

Primary and secondary

What type of solvent does an Sn2 reaction need and why?

Polar aprotic because they can dissolve the salt-nucleophile structure, but doesn’t hinder reactivity of nucleophile (also prevents solvation effect)

Polar aprotic

Compound has no acidic hydrogens

Solvation effect

Interaction of a solute with the solvent that leads to stabilization of the solute

What type of alkyl halide(s) does an Sn1 reaction happen on?

Tertiary

Kinetics of Sn1 Reaction

First order, Rate= K [R-X]

How many transition states does Sn1 have?

3

How many intermediates does Sn1 have?

2

Are Sn1 Nucleophiles weak or strong?

Weak

What type of solvent does an Sn1 reaction need?

Polar protic

Polar protic

Contains acidic hydrogens and/or hydroxyl groups (solvent acts like nucleophile, called solvolysis)

Stability of carbocations

Tertiary > Secondary > Primary > Me

Carbocations have what type of structure, making them a Racemic mixture?

Trigonal planar

Carbocations can _ to form the most stable product

rearrange

Priority goes to the atom with the highest _

atomic number

(E) Configuration

German for entgegen (“opposite”)

(Z) Configuration

German for zusammen (“together”)

How do you assign the stability of alkenes?

Less stable= terminal alkenes, More stable= Internal alkenes

Dehydrohalogenation

A way of synthesizing alkenes by eliminating Hx from an alkyl halide

What mechanism does an E2 reaction use?

Concerted

What is different about an E2 reaction?

Instead of a nucleophile, elimination uses a strong base

Alkoxide Base Synthesis

Typically uses an alcohol and Na or K

What does EtONa mean?

Sodium ethoxide

What does EtOH mean?

Ethanol

What is the kinetics of an E2 reaction?

2nd order, Rate= [sub] [base]

What type of alkyl halide does E2 react best with?

Tertiary

What is the stereoselectivity of E2?

The preference of one stereoisomer over another

Antiperiplanar (Anti-coplanar)

Hydrogen and leaving group are 180 degrees apart

Synperiplanar (Syn-coplanar)

Hydrogen and leaving group are 0 degrees apart

What are examples of strong bases in E2 reaction?

-OH (KOH), -OR (NaOEt), t-buO- (t-butOK)

Regioselectivity

Double bond in the product can be formed in more than one place

Zaitsev product

Most substituted

Hoffmann product

Least substituted

What does the base being used in an E2 reaction determine?

Major and minor products

Bulky bases

Favor the Hoffman product

Non-bulky bases

Favor the Zaitsev product

What type of mechanism and why type of base is in an E1 reaction?

Stepwise and weak

What is the kinetics of an E1 reaction?

1st order, Rate= K [Sub]

E1 can only react with a _ alkyl halide

Tertiary

Types of weak bases in an E1 reaction?

H2O, ROH (MeOH or EtOH), COOH

How do you determine what reaction is taking place?

Determine the function of the reagent (elimination or substitution) and look at your substrate to determine the mechanism (base type, nucleophile type, and alkyl halide type

Acidic conditions can push alcohols into an _ rxn.

elimination

Dehydration

Water leaving group (protonation of an alcohol)

Catalysts Rule

Catalysts must always be conserved at the end of a reaction

Regioselectivity

Zaitsev always

Dehydrating tertiary and secondary alcohols is what reaction?

E1

Dehydrating primary alcohols is what reaction?

E2

Charge

The more negative charge, the better the nucleophile

Electronegativity

less electronegative atoms are good nucleophiles

What is the relationship between electronegativity and nucleophilicity?

Inverse relationship

Sterics

The smaller the nucleophile, the better it is

To determine acid-base principle _

look at the conjugate acid