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39 Cards in this Set

  • Front
  • Back
What are the four categories that virtually all organic reactions fall into?
substitutions, additions, eliminations, and rearrangements
What are substitutions? And are characteristic of what kind of compounds?
reaction in which one group replaces another; characteristic of saturated compounds such as alkanes and alkyl halides, and of aromatic compounds
What are additions?
Reaction in which all parts of the adding reagent appear in the product; two molecules become one

characteristic of compounds with multiple bonds
What are eliminations?
Reaction in which one molecule loses the elements of another small molecule.
What is a rearrangement?
Reaction in which a molecule undergoes a reorganization of its constituent parts
What is heterolysis?
A covalent bond breaking so that one fragment takes away both electrons of the bond, leaving the other fragment with an empty orbital.

This produces ions and is called an ionic reaction.

Normally requires that the bond be polarized.
What is homolysis?
A covalent bond that breaks so that each fragment takes away one of the electrons of the bond.

This produces fragments with unpaired electrons called radicals.
How does heterolysis occur?
It occurs with assistance because even with a highly polarized bond heterolysis requires separation of oppositely charged ions that are very attracted to each other.

It is often assited by a molecule with an unshared pair that can form a bond to one of the atoms.
What is the Bronsted-Lowry theory?
an acid is a substance that can donate (or lose) a proton, and a base is a substance that can accept (or remove) a proton
What is a conjugate base?
molecule or ion that forms when an acid loses its proton
What is a conjugate acid?
the molecule or ion that forms when a base accepts a proton
What is the Lewis definition of acids and bases?
acids are electron pair acceptors and bases are electron pair donors
What are carbocations and carboanions?
a carbocation is an ion with a positive charge on the carbon atom

a carbanion is an ion with a negatively charged carbon atom
Why are carbocations Lewis acids?
Because they have only six electrons in their valence shell
What are electrophiles?
Reagents which in their reactions seek the extra electrons that will give them a stable valence shell of electrons.

eg. carbocations, all lewis acids, and protons
What are nucleophiles?
Reagents that seek a proton or some other positive center to neutralize their negative charge

eg. carbanions
What is the acidity constant, Ka?
Determines the acid strength. A large value of Ka means the acid is a strong acid and a small value of Ka means the acid is a weak acid.
What is pKa?
the negative logarithm of Ka; the large the value of the pKa, the weaker the acid.
How can the strength of bases be predicted?
The stronger the acid, the weaker its conjugate base.

Relate the strength of a base to the pKa of its conjugate acid. The larger the pKa of the conjugate acid, the stronger the base.
What is the general principle of predicting whether or not acid-base reactions will occur as written?
Acid-base reactions always favor the formation of the weaker acid and the weaker base because they are lowest in potential energy, and thus more stable.
What is the trend of proton acidity on a periodic table?
Proton acidity increases as we descend a column due to the decreasing bond strength to the proton
Describe the effect of hybridization on acidity.
Having more s character means that the elecrons of the anion will, on average, be lower in energy, and the anion will be more stable.

(eg. sp orbitals have 50% s character while sp3 orbitals have 25% s character, therefore the sp orbital will be more stable)
What is an inductive effect?
The electron-attracting or electron withdrawing ability of an atom transmitted through space and through the bonds of the molecule.

They weaken as the distance from the substituent increases.
What is relative stability?
The relative stability of a system is inversely related to its relative potential energy.

The more potential energy an object has, the less stable it is.
What is the change in potential energy of atoms when a chemical bond is formed between them?
potential energy is lowered
What is enthalpy change?
The difference in relative enthalpies of reactants and products in a chemical change; symbolized by delta H

negative delta H = exothermic rxn
positive delta H = endothermic rxn
What is the equation for free energy change (delta G)
delta G = -RT ln Keq

R= 8.314 J/K/mol
T = absolute temperature in K
What does a negative value of delta G mean?
Means that the reaction favors the formation of products when equilibrium is reached, and for which the equilibrium constant is greater than 1
What does a positive value of delta G mean?
Means that a reaction for which the formation of products at equilibirum is unfavorable, and for which the Keq is less than 1.
What is the relationship between free-energy change, enthalpy change, and entropy change (delta S)
delta G = (delta H) - T(delta S)
What is the trend of delta H for acid strength?
the less positive or more negative the value of delta H, the stronger the acid will be
What is the significance of a positive entropy change?
Makes a negative contribution to delta G and is energetically favorable for the formation of products.
What is the inductive electron-withdrawing effect?
The two oxygen atoms in a carboxylate ion combine electronegativities and are more stable than a single electronegative oxygen atom. This results in carboxylic acid being a stronger acid than an alcohol.
What does the stabilization of the conjugate base of an acid result in?
it increases the strength of the acid
Why are most acids weaker in the gas phase?
Because when an acetic acid molecule donates a proton to a water molecule in the gas phase, the ions that are formed at oppositely charged particles and the particles must become separated.

In the absence of a solvent, separation is difficult. Solvent molecules surround the ions, insulated them from one another, stabilizing them, and making them easier to separate.
What is a protic solvent?
A solvent that has a hydrogen atom attached to a strongly electronegative element such as oxygen or nitrogen.

eg. water
Why does solvation increase acidity?
Because solvation of any species decreases the entropy of the solvent, so solvent molecules become much more ordered as they surround molecules of the solute.
What is a protonated alcohol?
the conjugate acid of an alcohol
What is the leveling effect?
When water donates a proton to any base stronger than a hydroxide ion.

Bases stronger than hydroxide ion cannot be used in aqueous solution. Stronger bases can be used if we choose solvents that are weaker acids than water.