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60 Cards in this Set
- Front
- Back
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What is nucleophilic substitution?
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Any reaction in which an electron-rich group replaces a leaving group.
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What is a beta-elimination?
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A reaction in which a halide and hydrogen on a neighboring (beta) carbon are removed.
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In an Sn2 reaction, bond breaking and bond making occur _______?
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Simultaneously.
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What does the 2 stand for in Sn2?
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Bimolecular.
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What type of reaction utilizes the backside attack?
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Sn2
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How many peaks are found on a reaction diagram for an Sn2 reaction?
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1
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How many peaks are found on a reaction diagram for an Sn1 reaction?
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2
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Does an Sn2 reaction produce intermediates?
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No.
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Does an Sn1 reaction produce intermediates?
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Yes, a carbocation.
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What is the rate determining step in an Sn1 reaction?
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Formation of the carbocation.
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In an Sn1 reaction between a carbocation and methanol, does methoxide attack the carbocation?
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No! The deprotonation from the hydroxyl group occurs last.
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How many electrons does a carbocation have?
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6
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What rate order is an Sn1 reaction?
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First order
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The rate of an Sn2 reaction is dependent on what?
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The electrophile and nucleophile and is thus second order.
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Doubling the concentration of the nucleophile in an Sn1 reaction will affect the rate how?
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It won't.
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Doubling the concentration of the nucleophile in an Sn2 reaction will affect the rate how?
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It will double.
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In an Sn1 reaction taking place at a chiral center, what will the product show?
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Racemic mixture.
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In an Sn2 reaction taking place at a chiral center, what will the product show?
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Conversion from R to S or S to R.
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Why might an Sn1 reaction produce a partially racemic mixture?
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Even though the nucleophile can attack from either side, it might be less sterically hindered from one side over the other.
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What is the main determinate in the rates of Sn1 reactions?
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The stabilities of carbocation intermediates.
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What is the main determinate in the rates of Sn2 reactions?
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Steric factors at the reaction site. Bulky groups such as T-butyl will virtually stop progression of the reaction.
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What type of carbon forms the most stable carbocation?
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Tertiary.
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A carbocation is a ________ intermediate?
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High-energy.
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Will an allyl form a good carbocation?
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Yes because the charge can be spread across two carbons essentially. Draw the contributing structures.
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Are benzylic carbocations stable?
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Yes because the positive charge can be spread across the entire ring.
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Can methyl form a stable carbocation?
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No
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Will an Sn1 reaction occur with SP2 carbons?
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Rarely, and never with SP carbons because the carbocations are two unstable.
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What form the best leaving groups?
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The most stable anions.
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The best leaving groups are formed by what chemical class?
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Weak conjugate bases of strong acids.
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What are the two main classes of solvents?
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Protic and aprotic.
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What is the dielectric constant?
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A measure of a solvent's ability to undulate opposite charges from each other.
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Which will solvate better, a solvent with a high or low dielectric constant?
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High because it will allow for less interaction between ions of opposite charge dissolved in it.
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What is a polar solvent in terms of dielectric constants?
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15 or great on the dielectric scale.
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What is a nonpolar solvent in terms of dielectric constants?
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5 or less on the dielectric scale.
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Is water protic or aprotic?
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Protic.
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A protic solvent is a solvent that is a ________ donor.
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Hydrogen-bond
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What is DMSO?
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Dimethyl sulfoxide is a polar, aprotic solvent.
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What is DMF?
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Dimethyl formamide is a polar, aprotic solvent.
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What is acetone in terms of solvents?
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A polar, aprotic solvent.
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What solvents are best for Sn1 reactions?
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Polar protic solvents that can stabilize the carbocation and keep it separated from the negatively charged leaving group.
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What solvent is best for Sn2 reactions?
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Polar, aprotic solvents are best because while they can solvate cations well, there is no hydrogen to hydrogen bond the anion (nucleophile).
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What is nucleophilicity?
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It is a kinetic property which is measured by the relative rates of reactions.
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Within a period, nucleophilicity increases from _____ to ______ because (when in water or alcohol)?
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Top; bottom even though basicity increases from bottom to top because size increases from top to bottom and a large molecule is less solvated by polar protic water or alcohol than a small molecule.
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Within a row, nucleophilicity increases from _____ to _____ because?
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From right to left because basicity increases.
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During collisions _____ energy is converted to _____ energy stored in _____?
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Kinetic; potential, structural strains.
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A transition state possesses partially broken and partially formed _____?
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Bonds
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A concerted process is a _____ process?
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One-step
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Can inversion take place without a change from R to S (vice versa)?
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Yes if the priorities of the attached groups are changed between the starting materials and the products.
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What is a hydrogen bond donor?
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The molecule to which the hydrogen atom is covalently bonded.
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What is a hydrogen bond acceptor?
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The molecule bearing the unshared pair of of electrons to which hydrogen is partially bonded.
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A protic solvent is a _______ bond donor?
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Hydrogen
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Polar protic solvents are very effective at solvating _____ by hydrogen bonding?
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Anions
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Polar aprotic solvents are very effective at solvating _____?
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Cations.
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A nucleophile must be at least partially removed from its _____ to participate in Sn2 reactions?
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Solvent shell.
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An Sn2 reaction occurs faster in (protic, aprotic) solvents because?
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Aprotic because the anion is less solvated so less energy is required to remove it from it's solvent shell.
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In aprotic conditions, halide nucleophilicity increases from _____ to ____ because?
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Bottom to top because electronegativity increases from bottom to top and the anion is not highly solvated.
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In protic conditions, halide nucleophilicity increases from _____ to _____ because?
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Top to bottom because the smaller fluorine molecule is highly solvated and therefore requires a great amount of energy to break out of it's solvent shell to participate in chemistry.
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What is the geometry of a carbocation?
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Trigonal planar.
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The unhybridized 2p orbital lies _____ to the sigma framework and contains _____ electrons in a carbocation?
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Perpendicular; no.
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What is a 1,2 shift?
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A rearrangement in which at atom, or group of atoms, with its bonding electrons moves from one atom to an adjacent electron-deficient atom.
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