Organic Chemistry Answers

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The Four types of organic reactions
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substitutions, additions, eliminations, rearrangements
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a Mechanism for the reaction
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a desription of the events that take place on a molecular level as reactants become products.
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heterolysis
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The breaking of a covalent bond in which one fragment takes both electrons, leaving the other with an empty orbital
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Homolysis
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The breaking of a covalent bond in which each fragment takes one of the electrons.
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Radicals
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Fragments with unpaired electrons from homolytic cleavage.
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True or False: Heterolysis normally requires that the bond to be broken is polarized.
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True.
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Why does heterolysis require input of energy?
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Because heterolysis involves the separation of oppositely charged ions.
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Bronsted-Lowry Acid
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a substance that donates (or loses) a proton.
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Bronsted-Lowry Base
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A substance that accepts (or removes) a proton.
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What are the products of the acid-base reaction between water and hydrogen chloride?
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Hydronium ion (H3O+) and chloride anion (Cl-)
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In the reaction between water and hydrogen chloride, which is the acid? Which is the base?
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Water is the base, HCl is the acid.
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In the reaction between water and hydrogen chloride, what is the conjugate acid? What is the conjugate base?
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H3O+ is the conjugate acid, and Cl- is the conjugate base.
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Organic chemistry studies which more often: Bronsted-Lowry or Lewis acids and bases?
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Lewis.
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Lewis Acid
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an electron pair acceptor
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Lewis Base
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an electron pair donator
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Any electron deficient atom can act as a Lewis (acid/base)
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Lewis acid (an electron pair acceptor)
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True or False: carbocations are electron deficient.
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True
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How is a carbocation formed?
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Heterolysis of a bond to a carbon atom. The electron pair goes to the non-carbon element.
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Carbocations have how many valence shell electrons?
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Six.
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Carbocations are Lewis Acids or Lewis Bases?
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Lewis acids. They are electron deficient and accept electron pairs.
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True or False: Carbocations are generally stable and unreactive.
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False- carbocations are HIGHLY reactive.
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Carbocations are electron-seeking reagents, therefore chemists call them __________.
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electrophiles
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All Lewis acids, including protons, are (electrophiles/nucleophiles)
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Electrophiles.
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True or False: In contrast to the hydrochloric acid (HCl) and sulfuric acid (H2SO4), acetic acid (CH3COOH) is a much stronger acid.
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False, acetic acid (CH3COOH) is a much weaker acid than HCl or H2SO4
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Ka is an indicator of acid strength. The greater the Ka, the (stronger/weaker) the acid.
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Large Ka means Strong acid.
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What is the equation for the acidity constant of a reaction of an acid in aqueous solution?
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Ka = [H3O+][A-] / [HA]
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How does pKa relate to Ka?
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pKa = -log Ka
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The larger the value of the pKa, the (stronger/weaker) is the acid.
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A LARGER pKa indicates a WEAKER acid.
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Is acetic acid (CH3COOH) a strong or weak acid?
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Acetic acid is a relatively weak acid. pKa = 4.75
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Is ethane a strong acid or a weak acid?
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Ethane (CH3-CH3) is a VERY WEAK acid.
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The stronger the acid, the (stronger/weaker) its conjugate base.
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A strong acid has a WEAK conjugate base.
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The larger the pKa of a conjugate acid, the (stronger/weaker) the base.
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A large pKa of a conjugate acid (the base plus H) indicates a STRONG base.
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Water has a pKa = 15.7. What is water’s conjugate base, and is it a strong or weak base?
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Water’s conjugate base is OH-, and the large pKa of water indicates that water is a weak acid and OH- is a VERY STRONG base
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True/False: Amines are like ammonia in that they are strong bases.
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False- amines and ammonia are weak bases.
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A strong base has a conjugate acid with a (high/low) pKa.
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A high pKa.
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Acid/base reactions always favor the formation of the (stronger/weaker) acid and base.
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Acid/base reactions always favor the formation of the weaker acid and the weaker base.
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True/False: Acetic acid and other carboxylic acids containing fewer than 5 carbons are soluble in water.
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True.
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Carboxylic acids of high molecular weight do not readily dissolve in water. They DO dissolve in _______?
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sodium hydroxide.
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Methyamine and other amines of low molecular weight dissolve in water. However, amines of high molecular weight such as aniline (C6H5NH2) do not readily dissolve in water. These water insoluble amines dissolve readily in __________?
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hydrochloric acid
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Why do heavy, water insoluble carboxylic acids and similar amines dissolve in solutions of NaOH and HCl, respectively?
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Because they react to form water-soluble salts.
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Acidity (increases/decreases) as we descend a column in the periodic table.
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acidity increases down a column.
HI>HBr>HCl>HF
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Which bond is stronger, HF or HI?
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The HF bond is the strongest hydrogen halide bond, and HF is the weakest hydrogen halide acid.
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What are the conjugate bases of HI, HBr, and HCl?
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I-, Br-, and Cl-. These are weak bases.
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What is the strongest acid: H2O, H2S, or H2Se?
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H2Se is the stronger acid because Se is farthest down the column in the periodic table, therefore the H2Se bond is the weakest.
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Acidity (increases/decreases) from left to right across a row of the periodic table. Why?
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Acidity increases across a row due to the increasing electronegativity.
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What is the weakest acid: CH4, NH3, H2O, HF?
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CH4 is the weakest acid because carbon has the lowest electronegativity, so the C-H bond is the least polarized, and the proton in the C-H is the least positive. So it’ll stay there.
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What is the strongest acid: CH4, NH3, H2O, HF?
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HF is the strongest acid because F has the highest electronegativity, therefore the H-F bond is the most polar, and the proton in H-F is the most positive, and will leave.
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Which is the strongest base: CH3-, H2N-, HO-, F-? Why?
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CH3- is the strongest base. Carbon is the least electronegative of these elements and is least able to accept the negative charge. CH3- will readily accept a proton to become neutral, and that makes it a strong base.
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Which is the weakest base: CH3-, H2N-, HO-, F-? Why?
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F- is the weakest base because F is the most electronegative element and will readily accept the negative charge. It doesn’t want a proton as much as the others.
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Which is most acidic: ethyne, ethene, or ethane? Why?
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Ethyne is the most acidic. The sp orbitals of the C-H bond have 50% s character, making the sp carbons of ethyne act as if they were more electronegative than the sp2 carbons of ethene and the sp3 carbons of ethane.
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Which is most acidic: ethyne, ethene, or ethane? Why?
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Ethyne is the most acidic. The sp orbitals of the C-H bond have 50% s character, making the sp carbons of ethyne act as if they were more electronegative than the sp2 carbons of ethene and the sp3 carbons of ethane.
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Which is most acidic: ethyne, ethene, or ethane? Why?
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Ethyne is the most acidic. The sp orbitals of the C-H bond have 50% s character, making the sp carbons of ethyne act as if they were more electronegative than the sp2 carbons of ethene and the sp3 carbons of ethane.
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A convenient way to represent the relative potential energies of molecules is in terms of their relative _________, or heat contents.
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enthalpies, H
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A negative value of free-energy change indicates that the reaction:
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favors the formation of products when equilibrium is reached, the reaction goes to completion.
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A positive value of free energy change (delta G) indicates that the reaction:
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does not favor the formation of products at equilibrium, Ka is less than one.
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For the ionization of an acid, the less positive or more negative the value of deltaH, the (stronger/weaker) the acid will be.
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STRONGER
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A positive entropy change (from order to disorder) makes a (positive/negative) contribution to deltaG and (is/is not) energetically favorable to the formation of products.
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NEGATIVE, IS FAVORABLE.
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Carboxylic acids are much (stronger/weaker) acids than the corresponding alcohol.
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Carboxylic acids are much STRONGER than the corresponding alcohols.
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Explain how carboxylic acids are stronger than the corresponding alcohols in terms of resonance theory.
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Two resonance structures can be written for a carboxylic acid and two for its anion. Those for the acid are not equivalent and one requires charge separation. Both of those facts require energy. The two of the anion are equivalent and do not require charge separation, which lowers the free energy change and strengthens the acid. An alochol does not have these properties.
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Explain why carboxylic acids are stronger than the corresponding alcohols according to inductive effects.
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The powerful electron-attractive inductive effect of the carbonyl group makes the carbon of the C=O very positive, and it adds the inductive to the oxygen of the hydroxyl, which makes the proton more positive, and more likely to separate.
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Dispersal of charge always makes a species (more/less) stable.
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MORE stable.
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Dispersal of charge always makes a species (more/less) stable.
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MORE stable.
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What is a protic solvent?
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A solvent with a hydrogen atom attached to a highly electronegative atom like oxygen or nitrogen.

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