MCAT - Chemistry/Organic Chemistry

Equation for atomic number, mass number, and neutrons
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Periodic trends: Ionization energyIncreases to the top rightPeriodic trends: Electron AffinityIncreases (gets more negative) to the top rightPeriodic trends: ElectronegativityIncreases to the top rightPeriodic trends: AcidityIncreases to the bottom rightWhat is ΔH and what do positive/negative values mean?ΔH is enthalpy (the formation of heat) -ΔH = exothermic (releases heat) +ΔH = endothermic (absorbs heat)What is ΔG and what do positive/negative values mean?ΔG is gibbs free energy -ΔG = spontaneous +ΔG = nonspontaneousWhat is ΔS and what do positive/negative values mean?ΔS is entropy (a state of disorder) -ΔS = less disorder/randomness +ΔS = more disorder/randomnessThe oxidation state of any element in its standard state is _________?ZeroThe sum of the oxidation states of atoms in a molecule/ion must always equal the __________?Overall chargeWhat is a reducing agent?An electron donor; becomes oxidizedWhat is an oxidizing agent?An electron acceptor; becomes reducedWhat occurs at the cathode?Reduction Cations attract Plating occursWhat occurs at the anode?Oxidation Anions attract Pitting occursPauli Exclusion Principle?States that a maximum of two electrons can occupy a single atomic orbital but only if the electrons have opposite spinsAufbau Principle?The rule that electrons occupy the orbitals of lowest energy firstWhat is an inert gas?A gas that does not undergo a chemical reaction; noble gasesColoumb's Law?Refers to attractive force between any two charged particles F=kq1q2/r^2What is ionization energy?The energy required to remove an electron from an atomWhat is electronegativity?Ability of an atom to attract electronsDo metals typically lose or gain electrons in the presence of nonmetals?LoseWhat is acidity?A measure of the concentration of hydrogen ions (H+) in a solutionHow do you draw a Lewis Dot Structure?1. count the valence electrons 2. Arrange the atoms with the least electronegative atom in the center (C always goes to the center, H never does) 3. connect each atom with one line 4. add pairs of electrons to all non-hydrogen atoms until each has 8 (start with the most electronegative) 5. if there are remaining electrons, add them in pairs to the central atom 6. if there are missing octets, form db/tb 7. assign formal chargesBreaking a bond is a _______ process? Forming a bond is a _______ process?Endothermic; ExothermicIonic bonds are formed between?Oppositely charged ions (metals and nonmetals)What are ion-dipole forces?The attraction between an ion and a polar moleculeWhat is a dipole-dipole force?The attraction between the positive end of one polar molecule and the negative end of another; are easily brokenWhat is a dipole?Polar moleculeWhat is a dipole-induced dipole force?Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules by a dipole; are easily brokenWhat are London dispersion forces?The intermolecular attractions resulting from the constant motion of electrons and the creation of instantaneous dipolesWhat are Van der Waals forces?A slight attraction that develops between the oppositely charged regions of nearby moleculesList the intermolecular forces from strongest to weakestIon-dipole > Hydrogen bonds > Dipole-dipole > Induced-dipole > London dispersionWhat is a calorie?The amount of energy needed to raise the temperature of 1 gram of water 1 degree CelsiusWhat is a solute and solvent?Solvent: Substance that does the dissolving. Solute: Thing being dissolved.What are electrolytes usually insoluble in water?Ag+, Pb2+, Hg2+, Pb4+, Hg2 2+, CO3 2-, PO4 3-, S2-Dalton's Law of partial pressuresStates that the total pressure of a mixture of gases is equal to the sum of the pressures of all the gases in the mixtureWhich compounds travel farthest on a thin-layer chromatography (TLC) plate?Nonpolar (amines/aromatics)Explain the difference between σ and π bondsσ bonds are the result of end-to-end overlap of orbitals and create single bonds. π bonds are the result of side-to-side overlap of orbitals and create double and triple bonds.Explain the difference between sp-, sp2-, and sp3-hybridized carbon atomssp-hybridized carbon atoms have two groups bonded to them and a 180 degree bond angle. sp2 = have three groups bonded and 120 degree angle. sp2 = have three groups bonded and 120 degree angle.To what does the term unsaturated refer?An unsaturated molecule contains one or more rings or pi bonds, such that it does not contain the maximum possible amount of hydrogen.Rank the four possible types of alkyl carbocations from least stable to most stable.Methyl, primary, secondary, and tertiaryWhat must be present in order for resonance to occur?A π bond, so that electrons can be delocalizedWhat is a chiral center?A carbon atom bearing four different substituentsExplain the difference between structural isomers, conformational isomers, and stereoisomersStructural isomers = two molecules that have the same molecular formula but different connectivities. Conformational isomers = have the same molecular formula but different in rotations about single bonds. Stereoisomers = have the same molecular formula and connectivities of atoms but the groups differ in their arrangements of the molecule.What is another name for geometric isomers?Geometric isomers are a type of diastereomer. They can also be referred to as cis/trans isomers about a double bond or ring.What are the two types of stereoisomers?Geometric isomers and optical isomersWhat is the most stable conformation of methylcyclohexane?The chair form with an equatorial methyl groupWhat is a racemic mixture?50/50 mixture of two enantiomersWhat is a Lewis acid and base?Acid - an electron pair acceptor Base - an electron pair donorWhat is a leaving group?A leaving group is a stable species that detaches itself from a molecule with its electron pair during the course of a reaction.Is inversion of configuration seen in an Sn1 or in an Sn2 reaction? Which yields a racemic mixture of products?Sn2; Sn1 yields a racemic mixtureWill a more substituted substrate favour the Sn1 or the Sn2 mechanism?Sn1, because the first step is the formation of a carbocation, and more substituted carbocations are more stableIs the rate of the Sn1 or Sn2 mechanism dependent on the nucleophile concentration?Sn2What type of isomers are tautomers?Structural isomersWhat is a hyride? How does it differ from a proton? How does it differ from a hydrogen atomA hyride is a H2-, a proton is H+, and a hydrogen is HWhat is an imine?The nitrogen equivalent to a ketone or aldehydeWhat type of mechanism is the saponification of a triglyceride?Saponification is the addition-elimination reactionName the carboxylic acid derivatives from least to most reactive.Amide, ester, acid anhydride, acid halideGive the approximate infrared stretching frequencies for the following functional groups: O-H, C=O, CCO-H: 3200-3600 cm-1 C=O: 1700 cm-1 CC: 1650 cm-1What structural information does an infrared spectrum show?The functional groups present in the moleculeWhat does the splitting in an 1H NMR spectrum indicate? What does the number of signals in the spectrum show?The number of nonequivalent hydrogens on the adjacent carbon atoms;Are molecules with five or less carbon atoms that also bear a polar functional group more soluble in the aqueous or the organic layer in an extraction?AqueousWhat functional groups can be manipulated in an extraction to alter the solubility of a molecule?Carboxylic acids, phenois (ArOH), and aminesDo polar molecules or nonpolar molecules have lower Rf values in a TLC experiment?Polar molecules have lower Rf valuesFor each of the following chromatographic techniques, name the property(s) that are key to the function of the technique: TLC, GC, SEC, affinity chromatography, and ion exchange chromatographyTLC: polarity GC: polarity and boiling point SEC: size Affinity Chromatography: IMF Ion Exchange Chromatography: charge and sizeUsing R for the side chain, write the general structure of an amino acidAre animal amino acids in the D or in the L configuration?LWhat are two common techniques to synthesize amino acids?The strecker and the gabriel-malonic ester synthesisWhich of the two functional groups of an amino acid is more basic?The amino groupWhat is the pKa of the carboxylic acid of an amino acid and a protonated amino group?2; 10What are the two common names for the bond linking two amino acid residues together in a protein?Amide bond or peptide bondIn carbohydrates in their pyranose form, the anomeric carbon is part of what functional group?The anomeric carbon is part of a hemiacetalWhat is the difference between acidity and bond dissociation energy for a C-H bond?Acidity is associated with heterolytic bond cleave, while bond dissociation energy is associated with homolytic cleavageExplain the difference between enantiomers and diasteromersTwo molecules are enantiomers if they are steroisomers that are nonsuperimposable mirror images of each other. Diasteromers are stereoisomers that are not enantiomersWhat are two cases in which solutions of molecules with chiral centers show no observed optical rotation?Racemic mixtures and meso compounds have an optical rotation of zero degreesTo what does the term resolution refer?The separation of a mixture of two enantiomersWhat rules should be followed when prioritizing substituents on a chiral center to assign absolute configuration?The Cahn-Ingold-Prelog rulesWhat are two common ways of making an -OH group a better leaving group?1) Protonate it with an acid in which it will fall off as water 2) make the negative charge on the oxygen more stable by making a tosylate or mesylate groupHow does the choice of nucleophile affect the likelihood that 2-bromopropane will undergo Sn1 vs. Sn2?Stronger nucleophiles favour Sn2 reactionsWhat is the difference between addition, substitution, and elimination?In addition, a π bond is broken and two new σ bonds form. In elimination, two σ bonds break and a new π bond forms (opposite of addition). In substitution, one σ bond is exchanged for another σ bond.Name two common hydride sourcesLiAlH4 and NaBH4 are reducing reagents; NaH and KH are hydride bases.How are Grignard reagents synthesized?RBr + Mg ---> RMgBrHow are imines synthesized?Ketone(aldehydes) + ammonia or 1 degree amine ----> iminesIn a 1H NMR spectrum, a signal integrates for 3H and is split into a triplet. What does this indicate about the structure of the molecule?There is a methyl group adjacent to a -CH2-groupIn an extraction, why are organic acids soluble in an aqueous basic solution?The acid gets deprotonated to form a salt and salts are water solubleWhich base is a better choice to selectively remove a carboxylic acid from a phenol in the organic layer during an extraction, NaHCO3 or NaOH?NaHCO3 because it will deprotonate only the stronger acid, leaving the phenol unaffectedWhat does pI represent?pI represents the pH at which the most zwitterion is presentCalculate the pI of a neutral amino acid that has a pKa value of 2.15 and 9.632.15 + 9.63 / 2 = 5.89Are the two common synthetic techniques to produce amino acids stereo- or non-stereoselective?Non-stereoselectiveExplain the difference between primary, secondary, tertiary, and quaternary protein structuresPrimary structure is the amino acid sequence. Secondary structure refers to the initial folding of the polypeptide chain stabilized by hydrogen bonds into alpha helix or beta sheets. Tertiary structure concerns interactions between amino acid side chains and are stabilized by hydrophobic/philic interactions. Quaternary structure describes the interaction between polypeptide subunits.Electrophoresis separates amino acids based on what property?Their chargeWhat is the difference between α- and β-anomers?If the hydroxyl is down (under the ring) it is an α-anomer. If it is up (above the ring), it is a β-anomer.Why does the Benedicts test indicate?Reducing sugars or the presence of an aldehyde or ketoneWhy do micelles form?Because the tails of the fatty acids are very hydrophobic and therefore, repelled by water, they aggregate into spheres called micelles.State the three properties of electromagnetic radiationFrequency, wavelength, and energyDefine quantizedSomething is quantized if it comes only in certain discrete sizesOne type of nuclear decay has three different modes. What are they?Beta Decay: β- (normal), β+ (positron emission), and EC (electron capture)What are the three kinds of covalent bonds?Normal (polar or nonpolar), metallic, and coordinateGive two other names for Lewis basesLigand, nucleophileWhat three geometric family names are associated with each type of hybridized orbitals?linear = sp trigonal planar = sp2 tetrahedral = sp3Name the various intermolecular forces, from strongest to weakestHydrogen bonds > dipole-dipole > london dispersionWhen energy is added to a substance, that energy can be used to do one of two physical things. What are they?Increase the temperature (kinetic energy) or cause a phase changeWhat two things does vapor pressure depend on?Temperature and intermolecular forcesWhen does a liquid boil?When the vapor pressure of the liquid equals the atmospheric pressureThe phase of a substance depends on what two properties besides intermolecular forces?Temperature and pressureWhat assumptions do we make about ideal gases?ideal gases are composed of molecules that take up no volume and experience no intermolecular forcesWhat do the constants a and b account for in the van der waal's equation for real gases?a = the intermolecular forces between gas molecules b = the molecular volume of gas particlesWhat conditions are indicated by the letters STP?1 atm and 0 degrees CelsiusWhat is the volume of one mole of an ideal gas at STP?22.4 litresDescribe, at the molecular level, what happens to a solid when it dissolvesSolute particles are separated and encapsulated by solvent molecules so that solute dissolvesWhat is the difference between an intermediate and a transition state?Intermediates are found at local energy min. in a coordinate graph, and transitions states are found at the max.What is the minimum energy required to start a reaction?The activation energyWhat three properties affect the rate of a reaction?Concentration (or partial pressure for gases), temperature, and activation energyWhat are two ways to determine the order of a rate law?1) A multi-trial experiment where the concentration of one reagent is changed at a time 2) Looking at the rate-determining step in a previously proposed mechanismWhat types of substances are included in an equilibrium constant expression, and what types of substances are excluded?Gases and aqueous species are always included, whereas liquids and solids are excludedState three ways to disturb or stress a chemical equilibrium1) Change the concentration of the reactants/products 2) Change the temperature 3) Change the volume of the container (thereby changing the pressure)What is the only way to change the value of the equilibrium constant?Change the temperatureName the strong acids and strong basesStrong acids = HCl, HBr, HI, HNO3, HClO4, H2SO4 Strong bases = group 1 hydroxides and oxides, metal amides, Ba/Sr/Ca hydroxidesDefine conjugate pairTwo molecules/ions that differ by one H+How is the pH of a strong acid calculated?pH = - log[H+] Which is the same as -log[acid] since strong acids completely dissociateGive three reasons why a titration might be performed1) To determine the concentration of an unknown acid or base 2) To create a buffer 3) To determine the pKa or pKbWhat is the equivalence point of a titration?The equivalence point has been reached when the same number of moles of acid and base have been mixedWhat is a buffer?A solution that minimizes the impact of the addition of an acid or base on the pH of the solutionWhat happens to the pH of a buffer when it is diluted and concentrated?Nothing - the pH does not change with the addition/removal of a solventIdentify standard state conditions for temperature and pressureTemperature = 25 degrees celsius Pressure = 1 atmWhen is the entropy of a substance equal to zero?When a pure element is solid at zero KName and define the two parts of electrochemical reactions based on electron transfer?Oxidation (loss of electrons) and reduction (gain of electrons)What does a positive reduction potential indicate?The reduction half-reaction is spontaneous, while the associated oxidation half-reaction (the reverse reaction is nonspontaneousWhich electrochemical cell type produces electricity from a spontaneous chemical reaction?Galvanic cells use spontaneous reactions to produce electricity (electrolytic cells use electricity to force nonspontaneous reactions to occur)What is the sign of each electrode in a galvanic and electrolytic cell?Galvanic cell: cathode is positive, anode is negative Electrolytic cell: cathode is negative, anode is positiveGive two examples of elements that do not obey the Aufbau principleChromium (Cr) and copper (Cu)Explain the difference between paramagnetic and diamagnetic elements and give an example of eachParamagnetic atoms have unpaired electrons and diamagnetic atoms have all their electrons pairedWhat happens to the spacing between successively higher energy levels in an atom as you move farther away from the nucleus?It decreasesDescribe each type of nuclear decayAlpha, Beta (3 types), Gamma Alpha = reduces the parents atomic number by 2 and the mass number by 4 Beta - = converts a neutron into a proton and electron which is ejected, mass number remains the same Beta + = converts a proton into a neutron and positron, which is ejected Electron capture = atomic number is reduced by 1, mass number stays the same Gamma = have neither mass or charge, it is simply an expulsion of energyWhat type of mathematical relationship is associated with all radioactive decay?All radioactive elements decay exponentially with timeWhy is the mass of a nucleus not equal to the mass of the individual protons and neutrons that comprise it?Because the binding energy that is released when the nucleons are bound together in the nucleus comes from the mass defectDefine each periodic trendAtomic radius: extent of the valence electrons of an atom Ionization energy: energy required to remove a mole of valence electrons from a mole of gaseous atoms of a given element Electron affinity: energy associated with adding a mole of electrons to the valence shell of a mole of gaseous atoms of a given element Electronegativity: a measure of the amount of "pull" an atom has on shared valence electrons in a bond Acidity: the tendency for a molecule to give up a hydrogen ionWhat charge is generally associated with larger ions and smaller ions?Larger ions are negative, and smaller ions are positiveName at least three properties of liquids that depend on intermolecular forcesSolubility, vapor pressure, boiling point, melting point, viscosity, surface tensionWhat quantity is specified by the average kinetic energy of the molecules of a substance?TemperatureWhat are the official names for the six phase changes?Fusion, freezing, vaporization, condensation, sublimation, depositionWhat happens at the molecular level when a substance changes phases?Intermolecular forces are either broken or formedWhat property is used to measure the amount of a given gas in a mixture of gases?Partial pressureGive an example of a gas that most closely approaches ideal behaviourHeliumWhat temperature and pressure conditions allow most gases to behave most ideally?High temperature and low pressureWhat usually happens to the solubility of solids in liquids as the temperature is increased and why?Solubility increases at higher temperatures because solute-solute intermolecular forces weaken as solute molecules spread out due to increased vibrationHow does the solubility of gases in liquids depend upon temperature and pressure?The solubility of gas decreases with high temperatures but increases with high pressureWhich ions always result in a soluble salt? Which ions generally form insoluble salts?Group 1, ammonium, nitrate, acetate, and bicarbonate salts are always soluble in water Pb, Ag, and Hg salts are generally solubleWhat does the order of the rate law say about the reaction mechanism?The number of molecules colliding in the rate-determining stepHow does the rate of a chemical reaction change with temperature?Reaction rate always increases with increasing temperatureWhat two pieces of information are needed to calculate the pH of a weak acid?The Ka of the acid and the acid concentrationWhat information is needed to predict the pH at the equivalence point of a titration?The strengths of the acid and base being mixedDescribe two ways to make a buffer1. Add (roughly) equal molar amounts of a weak acid and a salt of its conjugate base (or a weak base and the salt of its conjugate acid). 2. Neutralize half of a sample of a weak acid (or base) by a strong base (or acid).How is the pH of a buffered solution calculated?By using the Henderson-Hasselbalch equation. The pH of a buffer is close to the pKa of the weak acid used, and the exact pH can be determined by taking the ratio of the conjugate base to acid into considerationWhen does pH = pKa for a buffer? What is this point called in a titration?When the concentrations of the weak acid and its conjugate base are equalHow are the common ion effect and the mechanism of a buffer related?They are the same thing (an application of Le Chatelier's Principle)What is the enthalpy of formation?The amount of energy associated with forming one mole of a compound from its constituent elements in their standard statesWhat three things must be considered to determine whether a reaction will happen or be spontaneous?Change in enthalpy, change in entropy, and temperatureDescribe the state of a reaction for which ΔG = zeroThe reaction is at equilibriumWhat kind of reaction occurs at the anode and cathode of an electrochemical cell?Oxidation occurs at the anode Reduction occurs at the cathodeWhat is the sign of the cell voltage in an electrolytic cell?NegativeWhat is the purpose of the salt bridge in a galvanic cell?To prevent charge separation as electrons move from one chamber to another. The salt bridges maintains charger neutrality in each chamber