set 2: organic chemistry and chemistry MCAT review

systems are classified based on what is or is not exchanged with the surroundings:

isolated

closed

open systems

I: exchange neither matter nor energy w the env

c: can exchange energy but not matter with the env

o: can exchange both energy and matter with the env

processes can be characterized based on a single constant property

isothermal

adiabatic

isobaric

isovolumeric (isochoric)

isotherm: processes occur at a constant temp

adia: processes exchange no heat with the env

isobar: processes occur at a constant pressure

isovol/isochor: processes occur at a constant volume

state functions

describe the physical properties of an equilibrium state; they are pathway independent and include pressure, density, temp, volume, enthalpy, internal energy, Gibbs free energy, and entropy

standard conditions

defined as 298 K, 1 atm, and 1 M concentrations

standard state of an element

is its most prevalent form under standard conditions; standard enthalpy, standard entropy, and standard free energy are all calculated under standard conditions

phase change:

fusion/freezing

vaporization/condensation

sublimation and deposition

exist at characteristic temperatures and pressures

fusion=melting, freezing=crystallization or solidification and both occur at the boundary between the solid and liquid phases

vaporization=evaporation or boiling, condensation and vap occur at the boundary between the liquid and gas phases

sub and dep occur at the boundary between the solid and gas phases

at temp above the critical point, (liquid and gas phases are…)

the liquid and gas phases are indistinguishable

at the triple point,

all three phases of matter exist in equilibrium

phase diagram

for a system of graphs the phases and phase equilibria as a function of temperature and pressure

temperature vs heat

not the same

temp: a scaled measure of the average kinetic energy of a substance

heat: is the transfer of energy that results from differences of temp between two substances

the heat content of a system undergoing heating, cooling, or phase changes is the sum of all the respective energy changes

enthalpy, how to calculate, and Hess’s law

is a measure of the potential energy of a system found in intermolecular attractions and chemical bonds

Hess’s law: states that the total change in pot energy of a system is equal to the changes of pot energies of the individual steps of the process

enthalpy can also be calculated using heats of formation, heats of combustion, or bond dissociation energies

entropy and when it is maximized

is a measure of the degree of to which energy has been spread throughout a system or between a system and its surroundings

entropy is a ratio of heat transferred per mole per unit kelvin

entropy is maximized at equilibrium

gibbs free energy (directionality of reaction in relation to G value)

is derived from both enthalpy and entropy values for a given system

the change in gibbs free energy determines whether a process is spontaneous or nonspontaneous

G<0 reaction proceeds in forward direction (spontaneous)

G=0 reaction is in dynamic equilibrium

G>0 reaction proceeds in reverse direction (nonspontaneous)

what does gibbs free energy depend on

temperature; temperature-dependent processes change between spontaneous and nonspontaneous dep on the temp

carbon adjacent to the carbonyl carbon is termed

alpha C; the hydrogens attached to the alpha C are also called alpha hydrogens

alpha-hydrogens: acidic or basic, and how can they thus be removed from the alpha C?

how is this able to occur?

are relatively acidic and can be removed by a strong base

the electric withdrawing O of the carbonyl weakens the C-H bonds on alpha-Carbons

enolate formation results from what

deprotonation of the alpha C, which can be stabilized by resonance with the carbonyl

ketones alpha H reactivity toward nucleophiles as compared to carbonyl alpha H

why is this?

less reactive toward nuc bc of steric hindrance and alpha-carbanion destabilization

the presence of an additional alkyl group crowds the transition step and inc its energy

the alkyl group also donates electron density to the carbanion, making it less stable

aldehydes and ketones exist in what two forms

the traditional keto form (C=O) and the less common enol form (ene + ol = double bond + hydroxyl group)

tautomers

are isomers that can be interconverted by moving a hydrogen and a double bond

the keto and enol forms are tautomers of each other

how enolate is formed

enol can be deprot and form an enolate

enolates are good nuc

the michael addition

an enolate attacks an alpha, beta-unsaturated carbonyl, creating a bond

kinetic vs thermodynamic enolate

K: is favored by fast, irreversible reactions at lower temps with strong, sterically hindered bases

T: is favored by slower, reversible reactions at higher temps with weaker, smaller bases

enamines

are tautomers of imnes

like enols, enamines are the less common tautomer

aldol condensation

the aldehyde or ketone acts as both nuc and elec., resulting in the formation of a C-C bond in a new molecule called an aldol

aldol

contains both aldehyde and alcohol functional groups

what is the nuc of an aldol condensation

what is the electriphile

the nuc is the enolate formed from the deprot of the alpha C

the elec is the aldehyde or ketone in the form of the keto tautomer

steps of aldol reaction (2 main steps and end product)

1—a condensation reaction occurs in which the two molec come together

2—after the aldol is formed, a dehydration reaction (loss of a water molec) occurs. this results in an alpha,beta-unsaturated carbonyl

retro-aldol reactions; what catalyzes it and what bond is cleaved

are the reverse of aldol condensations

are catalyzed by heat and a base

the bond between alpha- and beta- C is cleaved

the gas phase; what variables describe this phase

gases are the least dense phase of matter

gases are fluids and therefore conform to the shapes of their containers

gases are easily compressible

described by: temp (T), pressure (P), volume (V), and number of moles (N)

atm to mmHg to torr to kPa conversions

1 atm = 760 mmHG = 760 torr = 101.325 kPa

simple mercury barometer—what does inc in height mean ab pressure

measures incident (usually atmospheric) pressure

as pressure inc, more mercury is forced into the column, inc its height

as pressure dec, mercury flows out of the column under its own weight, dec its height

standard temperature and pressure (STP)

273 K (0 degrees C) and 1 atm

equations for ideal gases assume…

negligible mass and volume of gas molecules

ideal gases—regardless of its identity—when in equal molar amounts, will occupy the same… (which is what value)

regardless of identity of the gas, equimolar amounts of two gases will occupy the same volume at the same temp and pressure

at STP, one mole of ideal gas occupies 22.4 L

ideal gas law

describes the relationship between the four variables of the gas state for an ideal gas

avogadro’s principle

is a special case of the ideal gas law for which the pressure and temp are held constant; it shows a direct relationship between the number of moles of gas and volume

boyle’s law

is a special case of the ideal gas law for which temp and number of moles are held constant; it shows an inverse relationship between pressure and volume

charle’s law

is a special case of the ideal gas law for which pressure and number of moles are held constant; it shows a direct relationship between temperature and volume

gay-lussac’s law

is a special case of the ideal gas law for which volume and number of moles are held constant; it shows a direct relationship between temp and pressure

combined gas law

is a combination of boyle’s, charles’s, and gay-lussac’s laws; it shows an inverse relationship between pressure and volume along with direct relationships between pressure and volume with temp

dalton’s law of partial pressure

states that individual gas components of a mixture of gases will exert individual pressures in proportion to their mole fractions

the total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases

henry’s law

states that the amount of gas dissolved in solution is directly proportional to the partial pressure of that gas at the surface of a solution

kinetic molecular theory (and 5 assumptions)

attempts to explain the behavior of gas particles, it makes a number of assumptions ab the gas particle:

gas particles have negligible volume, do not have intermolecular attractions or repulsions, undergo random collisions with each other and the walls of the container, collisions between gas particles and the walls of the container are elastic, and the average kinetic energy of the gas particles is directly proportional to temp

graham’s law

describes the behavior of gas diffusion or effusion, stating that gases with lower molar masses will diffuse or effuse faster than gases with higher molar masses at the same temp

diffusion vs effusion

d: is spreading out of particles from high to low conc

e: is the movement of gas from one compartment to another through a small opening under pressure

real gases deviate from ideal behavior under:

—how will this deviation look and why

high pressure (low volume) and low temp conditions

at moderately high pressures, low volumes, or low temps, real gases will occupy less volume than predicted by the ideal gas law bc the particles have intermolecular attractions

at extremely high pressures, low volumes, or low temps, real gases will occupy more volume than predicted by the ideal gas law bc the particles occupy physical space

van der waals equation of state (and what 2 forces does it correct for)

is used to correct the ideal gas law for intermolecular attractions (a) and molecular volume (b)

carboxylic acids structure

contain a carbonyl and a hydroxyl group connected to the same carbon

they are always terminal groups

carboxylic acid nomenclature

indicated with the suffix -oic acids

salts are named with the suffix -oate

dicarboxylic acids are -odic acids

physical properties of carboxylic acids

-polarity and bonding tendencies

-acidity and how is this enhanced/decreased

-alpha H on dicarboxy

polar and hydrogen bond very well, resulting in high boiling points

they often exist as dimers in solution

the acidity is enhanced by the resonance between its oxygen atoms

acidity can be further enhanced by substituents that are electron withdrawing, and decreased by substituents that are electron-donating

beta-dicarboxylic acids, like other 1,3-dicarbonyl compounds have an alpha-hydrogen that is also highly acidic

how are carboxylic acids made

by the ox of primary alc or ald using an ox agent like potassium permanganate (KMnO4), dichromate salts (Na2Cr2O7 or K2Cr2O7), or chromium trioxide (CrO3)

nucleophilic acyl substitution process and name of products (3) based on type of nuc attacking

is a common reaction in carboxylic acids

a nuc attacks the electrophilic carbonyl C, opening the carbonyl and forming a tetrahedral intermediate

the carbonyl reforms, kicking off the LG

if the nuc is ammonia or an amine, an amide is formed (-amide or cyclic amides “lactams”)

if nuc is an alc, an ester is formed (-oate or cyclic esters “lactones”)

if nuc is another carboxylic acid, an anhydride is formed (“anhydride”)

how are carboxylic acids reduced (& what does int. look like)

to a primary alc with strong red agents like lithium aluminum hydride (LiAlH4)

ald int. are formed but are also red to primary alc

sodium borohydride (NaBH4) is a common red agent for other organic reactions, but IS NOT strong enough to red a carboxylic acid

spontaneous decarboxylation (& what does int. look like)

beta-dicarboxylic acids and other beta-keto acids can undergo spontaneous decarboxy. when heated, losing a carbon as CO2

this reaction proceeds via a six membered cyclic int.

mixing long chain carboxylic acids (fatty acids) with a strong base results in…

the formation of a salt (soap). this process is called saponification

soaps and micelle properties

soaps contain hydrophilic carboxylate heads and hydrophobic alkyl chain tails

soaps organize in hydrophilic envi. to form micelles (a micelle dissolves nonpolar organic molecules in its interior, and can be solvated w/ water due to its exterior shell of hydrophilic groups)

solutions

are homogeneous mixtures composed of two or more substances

they combine to form a single phase, generally liquid phase

solvent, solute, and solvation/dissolution

solvent particles surround solute particles via electrostatic interactions in a process called solvation or dissolution

most dissolutions are endothermic, although the dissolution of gas into liquid is exothermic

aqueous solutions

solvation in water can also be called hydration

solubility (& molar solubility definition)

is the maximum amount of a solute that can be dissolved in a given solvent at a given temp;

it is often expressed as molar solubility—the molarity of the solute at saturation

complex ions/coordination compounds and ligands

are composed of metallic ions bonded to various neutral compounds and anions, referred to as ligands

the process of forming a complex ion involves…

how does its formation impact solubility?

electron pair donors and electron pair acceptors, such as those seen in coordinate covalent bonding

formation of complex ions inc the solubility of otherwise insoluble ions (the opposite of the common ion effect)

ways to express concentration: percent composition by mass, mole fraction, molarity, molality, and normality

% comp by mass: (mass of solute per mass of solution times 100%) is used for aqueous solutions and solid-in-solid solutions

mole fraction: (moles of solute per total moles) is used for calculating vapor pressure depression and partial pressures of gases in a system

molarity: (moles of solute per liters of solution) is the most common unit for conc. and is used for rate laws, the law of mass action, osmotic pressure, pH and pOH, and the nernst eq.

molality: (moles of solute per kilograms of solvent) is used for boiling point elevation and freezing point depression

normality: (number of equivalents per liters of solution) is the molarity of the species of interest and is used for acid-base and oxidation-reduction reactions

saturated solutions means what ab equalibrium

are in equilibrium at that particular temp

solubility product constant (Ksp)

is simply the equilibrium constant for a dissociation reaction

comparison of the ion product (IP) to Ksp

determines the level of saturation and behavior of the solution:

IP<Ksp : the solution is unsaturated, and if more solute is added, it will dissolve

IP=Ksp : the solution is saturated (at eq) and there will be no change in conc

IP<Ksp : the solution is supersaturated, and precipitation will form

formation of a complex ion in solution greatly inc solubility, greatly dec solubility, or has no effect on solubility

greatly inc solubility

the formation or stability constant (Kf) definition and when compared to Ksp

how this process functionally can occur (compare to common ion effect)

is the eq. constant for complex formation

its value is usually much greater than Ksp

the formation of a complex inc the solubility of other salts containing the same ions bc it uses up the products of those dissolution reactions, shifting the eq to the right (the opp of the common ion effect!)

common ion effect

dec the solubility of a compound in a solution that already contains one of the ions in the compound

the presence of that ion in solution shifts the dissolution reaction to the left, dec its dissociation

colligative properties

are physical properties of solutions that dep on the conc of dissolved particles, but NOT their chemical identity

vapor pressure depression following Raoult’s law

& how it explains boiling point elevation

the presence of other solutes dec the evaporation rate of a solvent w out affecting its condensation rate, thus dec its vapor pressure

vapor pressure depression also explains boiling point elevation—as the vapor pressure dec, the temp (energy) required to boil the liquid must be raised

freezing point depression and boiling point elevation dep on what

are shifts in phase equilibria dep. on the molality of the solution

osmotic pressure is dep on what

is primarily dep on the molarity if the solution

van Hoff’s factor (i)

for solutes that dissociate, “i” is used in freezing point depression, boiling point elevation, and osmotic pressure calculations

amides

are the condensation products of carboxylic acids and ammonia or amines

amide nomenclature (general, alkyl groups on substituted amide, and cyclic)

given the suffix -amide

the alkyl groups on a substituted amide are written at the beginning of the name with the prefix N-

cyclic amides are called lactams. lactams are named by the greek letter of the carbon forming bond with the nitrogen (betta, gamma, etc)

esters—name and type of reaction that forms this product

are the condensation products of carboxylic acids with alcohols (fischer esterification)

cyclic ester naming

lactones

named by the number of carbons in the ring and the greek letter of the carbon forming the bond with the oxygen (alpha, beta, etc)

triacylglycerols (what it is and type of bonds it forms within itself)

which are a form of fat storage, include three ester bonds between glycerol and fatty acids

saponification/soaps

saponification is the breakdown of fat using a strong base to form soap (salts of long-chain carboxylic acids)

anhydrides & their naming (symmetric/asymmetric)

are the condensation dimers of carboxylic acids

symmetric anhydrides are named for the parent carboxylic acid, followed by “anhydride”

asymmetric anhydrides are named by listing the parent carboxylic acids alphabetically, followed by “anhydride”

how are cyclic anhydrides synthesized

some can be synth by heating dioic acids

five or six membered rings are generally stable

in nucleophilic substitution reactions, what is the order of inc reactivity:

amides, anhydrides, and esters

amides<esters<anhydrides

steric hindrances

describe when a reaction cannot proceed (or significantly slows) bc of substituents crowding the reactive site

protecting groups and how this is impacted by steric hinderence

such as acetals can be used to inc steric hindrance or otherwise dec the reactivity of a particular portion of a molecule

induction & what situation inc it

refers to uneven distribution of a charge across a sigma bond bc of diff in electronegativity

the more electroneg groups in a carbonyl-containing compound, the greater its reactivity

conjugation & what situation inc reactivity

refers to the presence of altering single and multiple bonds, which creates delocalized pi electron clouds above and below the plane of the molecule

electrons experience resonance through the unhybridized p-orbitals, inc stability

conjugated carbonyl-containing compounds are more reactive bc they can stabilize their transition states

strain (& ring strain) and reactivity

inc strain in a molec can make it more reactive

beta-lactams are prone to hydrolysis bc they have sig. ring strain

ring strain is due to torsional strain from eclipsing interactions and angle strain from compressing bond angles below 109.5 degrees

nucleophilic substitution reactions and carboxylic acid derivs. and what det. their reactivities

all carbox acid derivs can undergo nuc sub reactions

the rates they do so are det. by their relative reactivities

anhydrides and addition of a nuc, amine, alcohol, and water

can be cleaved by addition of a nuc

addition of ammonia or an amine results in an amide and a carboxylic acid

addition of alc results in an ester and a carboxylic acid

addition of water results in two carboxylic acids

transesterfication

is the exchange of one esterifying group for another on an ester

the attacking nuc is an alcohol

amides

can be hydrolyzed to carboxylic acids under strongly acidic or basic conditions

the attacking nuc is water or the hydroxide anion

arrhenius acids vs bases

a: dissociate to produce an excess of hydrogen ions in solution

b: dissociate to produce an excess of hydroxide ions in solution

bronsted-lowry acids vs bases

a: are species that can donate hydrogen ions

are species that can accept hydrogen ions

lewis acids vs bases

a: are electron pair acceptors

b: are electron pair donors

connections between arrhenius, bronsted-lowry, and lewis acids/bases

all arrhenius acids and bases are bronsted-lowry acids and bases and all bronsted-lowry acids and bases are lewis acids and bases

however, the converse of the statements is not necessarily true (not all lewis acids and bases are bronsted-lowry acids and bases, and not all bronsted-lowry acids and bases are arrhenius acids and bases)

amphoteric species

are those that can behave as an acid or base

amphiprotic species (and a classical example)

are amphoteric species that specifically can behave as a bronsted-lowry acid or base

water is an example of an amphoteric, amphiprotic species—it can accept a hydrogen ion to become a hydronium ion or it can donate a hydrogen ion to become a hydroxide ion

conjugate species of polyvalent acids and bases can also behave as… (accept/donate H+ and produce excess of said ions)

amphoteric and amphiprotic species