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Organic Chem II - Exam 2 Question Bank
A(n) ______ group contains sulfur bonded to hydrogen. - Thiol or mercapto Low temperatures are used to achieve- A) Thermodynamic control B) Reactant control C) Kinetic control D) Product control E) None of the above - C) Kinetic control What is the purpose of dimercaprol, and how does it work? - Dimercaprol is used to treat mercury and lead poisoning. Dimercaprol contains two thiol groups that can form metal complexes to bind to mercury and other toxic metals and remove them from the body. Why do equilibrium reactions favor the formation of reactants at high temperatures? - Using the Gibbs free energy equation, ΔG = ΔH - TΔS, will determine whether the reaction will favor reactants or products. In cases where only one of the terms is negative, temperature will determine which term has a greater magnitude which will cause ΔG to be negative or positive. In a synthesis reaction, entropy will be negative, the entropy term will be positive, and the temperature will determine whether that positive term is large enough to cause a positive ΔG (favors reactants). Therefore, a high temperature is needed to favor reactants. How can 2-methoxy-2-methyl-1-cyclohexanol be prepared from 3-methylcyclohexene? - 1) H2, Pt
- Br2, hν
- NaOEt
- mCPBA
- H2SO4, MeOH Sulfides are easily _______ and ______. - oxidized and make ideal reducing agents
which reagents will be needed for this reaction? (image on pg 1) a. i)NaH / ii) CH₃I b. Hv, MeOH c. i) Hg(OAc)₂, ROH / ii)NaBH₄ d. O₂ - c. i) Hg(OAc)₂, ROH / ii)NaBH₄ Thiols can occur with _________ with no competing reactions because ____ is an excellent nucleophile and a _____ base. - Secondary Alkyl Halides, -SH, Poor Which IUPAC name below represents the naming method where Oxygen is used as a substituent. a. 2-diethyl-3-dimethyloxirane b. 2,3-epoxy-3-ethyl-2-methylpentane c. 2,3-diethyl-3,3-dimethyloxirane d. 2,2-epoxy-3,3-dimethyloxirane - b. 2,3-epoxy-3-ethyl-2-methylpentane Why does the S=O bond have very little double bond character? - The 3p orbital of sulfur is larger than the 2p orbital of Oxygen and the orbital overlap of the population bond is not effective. Because of this, the double bond to Oxygen is often drawn as a single bond. Explain Thermodynamics control vs. Kinetic control - Thermodynamic control is done at elevated temps where competing pathways are reversible and there is enough energy to lose a leaving group and reform allylic+. Equilibrium is established and product distribution depends on the relative energy of the pdt. (Lower E=major product). Where as Kinetic control is done at low temps where the competing reaction pathways are irreversible and 1,2-addition occurs more rapidly. There is not enough energy to convert the 1,2-adduct back into allylic+. The product distribution is determined by relative rates. (Faster —> product) A conjugated polyene undergoes ____________. - cyclization
LUMO is an acronym for "lowest ________ molecular orbital." - unoccupied Hexatriene has 6 overlapping p orbitals which means it has a. 3 molecular orbitals b. 6 molecular orbitals c. 12 molecular orbitals d. 2 molecular orbitals - b. 6 molecular orbitals Explain why the HOMO is bonding and LUMO is anti-bonding. - LUMO is anti-bonding because there are no electrons present in the molecular orbitals, whereas, HOMO is bonding because it contains the highest energy electrons that are available to participate in a reaction. Autooxidation is the spontaneous oxidation of a compound when in the presence of what molecule? a. Carbon b. Oxygen c. Nitrogen d. NADH - b. Oxygen ____________ hindered substrates will reduce the Sn2 reaction rate. a. Chemically b. Radioactivity c. Sterically d. Monosubstituted - c. Sterically What does 'deshielding' mean in the context of NMR spectroscopy?
a. It refers to the electrons blocking a nucleus from an external magnetic field. b. It refers to the nucleus losing some of its electron density due to nearby electronegative atoms. c. It refers to a sample being energetically excited with RF energy d. It refers to unstable molecules decomposing in the NMR instrument if the magnetic field is too high - b. It refers to the nucleus losing some of its electron density due to nearby electronegative atoms. If a there is an SH group connected to an R group the product will be a ______ - Thiol The following molecule contains which functional group? (functional group = -SNa) a. Thiol b. Thiolate c. Sulfide d. Disulfide e. Sulfoxide f. Sulfone - b. Thiolate The LUMO of the first excited state for 1,3-butadiene has ___ vertical nodes. - 3 Why are there 9 ether groups in brevetoxin? - All of the rings in the compound except for the cyclopentane ring on the end of the structure contain an oxygen atom bonded to two alkyl groups. This adds up to a total of 9 ether groups. Explain how a deficiency of vitamin A , a source of 11-cis-retinal, can cause night blindness. - 11-cis- Retinal is a chromophore that reacts with the protein opsin to form the light-sensitive compound in rods called rhodopsin. The function of rhodopsin occurs through a cis-trans isomerization of 11-cis-retinal, which initiates a cascade of enzymatic reactions that culminates in a nerve impulse being sent to the brain. Sources of 11-cis-retinal include vitamin A and β-carotene. Therefore, a deficiency of vitamin A can cause night blindness.
What is an oxygen connected to two different R groups called? a. Unsymmetrical Ether b. Unsymmetrical Epoxide c. Symmetrical Ether d. Symmetrical Epoxide - a. Unsymmetrical Ether Explain a Diels-Alder reaction. - Diels-Alder is a chemical, concerted (one-step) reaction. This reaction involves a diene and a dienophile and 2 carbon-carbon sigma bonds form simultaneously to produce a substituted cyclohexene. Describe 3 analytical uses of UV-Vis spectroscopy. - 1. Often used in the structure elucidation of organic molecules. This in turn helps to determine whether conjugation is present in a given sample.
- Determining the concentration of an unknown sample by using known concentrations of a compound mixed in a solution containing the same solvent as the unknown.
- Used for quantitative analysis in biochemical studies. This is done so in order to measure the rates of enzymatic reactions. The less substituted alkene product forms more rapidly due to the ___________. - Proximity effect What is the IUPAC systematic name for (CH3)2CHOCH2(CH2)3CH3? a. 2-methoxy-2-methylheptane b. isopropyl pentyl ether c. 2,2-dimethylhexyl ether d. 1-isopropylpent-1-ether e. 1-isopropoxypentane - e. 1-isopropoxypentane
What is Kinetic control and what is its major product? - This is when the product distribution is determined by the relative rates. In Kinetic control the faster reaction is favored therefore the 1,2- adduct is the major product. When an ether is heated with a concentrated solution of a strong acid (HX), it will undergo acidic cleavage, in which the ether is converted into ______. - Two Alkyl Halides In a cycloaddition reaction, how many bonds are formed or broken (if any) and what types? - 2 sigma bonds are added, and 2 pi bonds are broken In a Diels Alder reaction, the temperature must be _____ in order to form the major product. a. High temperature (>100°C) b. Low temperature (<0°C) c. Moderate Temperature (0°<X<100°) d. Temperature doesn't matter in a Diels Alder reaction - c. Moderate Temperature (0°<X<100°) Owls can see very well at night and are colorblind. This means that owl eyes contain ________ only. - Rods Which color has the highest wavelength? a. Red b. Orange c. Yellow d. Green e. Blue f. Violet - a. Red What are the light-sensitive photoreceptor cells that detect color and work best in bright light? - There are two types of light-sensitive cells that function as photoreceptors: rods and cones. Cones contain the
What are the characteristics and definition of a Conjugated Diene? - Conjugated diene is a system of overlapping p orbitals. They have two pi bonds from four overlapping p orbitals that can have special properties and reactivity. In a few sentences, describe frontier orbitals. - Frontier orbitals are made of homo and lumo orbitals. A homo orbital contains the highest energy electrons that are readily available tp participate in a reaction. Lumo orbitals are the lowest energy molecular orbital that can accept electron density in a reaction. Dicyclopentadiene can not be stores at _____ ___________ because it converts to the ______ in a couple of hours. - room temperature, dimer Explain the Molecular Orbital Theory - We know that a π bond is constructed from overlapping p orbitals. According to MO theory, these two atomic p orbitals are mathematically combined to produce two new orbitals, called molecular orbitals. There is a difference between an atomic orbital and a molecular orbital. Specifically, electrons that occupy atomic orbitals are associated with an individual atom, while electrons that occupy a molecular orbital are associated with the entire molecule. According to MO theory, the two atomic p orbitals are replaced by two molecular orbitals. The antibonding MO exhibits a node that is absent in the bonding MO. The antibonding MO is higher in energy than the bonding MO. The π bond results from the ability of the π electrons to achieve a lower energy state by occupying the bonding MO. HOMO is the acronym for _____.HOMO is the acronym for _____. - Highest Occupied Molecular Orbital What is an isolated diene? - Two double bonds separated by more than one single bond Explain how the boiling points of ethers and alcohols differ and why. - Boiling points depend of the intermolecular forces. Alcohols have higher boiling points than ethers and because they can form hydrogen bonds. Ethers can't form hydrogen bonds and can only form dipole-dipole interactions with each other with London dispersion interactions. Unbranched alcohols also have higher boiling points than branched alcohols because they are able to form more dispersion interactions. _____________ double bonds are more stable than ________ double bonds. - conjugated, isolated Ethers are often used as ____________ for organic reactions. - Solvents
Ethers can be readily prepared from the reaction between an alkoxide ion and an______________________, a process called a Williamson ether synthesis. a.) phenol b.) alkyl halide c.) ketone d.) alcohol - b.) alkyl halide How can alkenes be converted into epoxides? - Alkenes can be converted into epoxides through the addition of peroxy acid or through the process of halohydrin formation and subsequent epoxidation. What are the 2 ways epoxides are named? - The first way is based on the oxygen atom of the compound, which is considered a substituent of the parent chain. In this method the parent chain is counted and then the substituent or oxygen atom is identified with two numbers indicating the exact location. These two numbers are followed by -epoxy. The second method that is used identifies the parent chain as the epoxide. Any groups or substituents connected to this parent chain, the epoxide are listed substituents in the name. ____ diene has adjacent pi bond. - Cummulated Why is the endo product favored in Diels Alders reaction? - The endo product is favored because the dienophile is under the diene and more available to react causing the product to endo or having the substituents being down. This also leads to the products to be closer to the larger bridge and being more favored. What kind of diene must appear for the reaction to occur? - The type of diene that must appear is a S-cis diene. This must occur because the reactants have to be close enough together to react. If the diene is in S-trans then the reactants would not be able to be reacted so the reaction would not be able to occur. The S-cis conformation is also more unstable than and S-trans conformations so this would be more likely to react. ____ utilizes a clockwise and counterclockwise rotation, while ____ has two counterclockwise rotations.
allylic carbocations. Therefore, product distribution depends on the relative energy of the products, and the 1,4-adduct has lower energy making it more stable. Explain the difference between a 1,2-adduct and a 1,4-adduct when adding X2 to 1,3-butadiene. - A 1,2- adduct is the addition of an X2 product across 1,3-butadiene in which one halogen is added to the first carbon of the double bond, and the other halogen is added to the second carbon of the double bond. Another product, a 1,4-adduct is created when the first halogen is added to the first carbon of the parent chain, and the second carbon is added to the fourth carbon of the parent chain of butadiene. Sulfur analogs of alcohols contain an SH group rather than an OH group and are called _______________. - thiols Why are ethers often used as solvents for organic reactions? - Ethers are fairly unreactive and dissolve a variety of organic compounds and also have low boiling points. Describe thiols from chapter 13. - Thiols contain SH group. SH is named as a substituent and is called a mercapto group. Thiols used to be called mercaptans. Derived from the Latin mercurium captans meaning capturing mercury. Thiols form complexes with hydrogen and other metals. Thiols have odors that are unpleasant and pungent. Thiols easily undergo oxidation to produce disulfides. Sulfides can also be prepared from thiols. An ether can act as a hydrogen bond acceptor by interacting with an _________. - Alcohol The HOMO of 1,3,5-hexatriene (in its ground state) has how many vertical nodes? a. 1 b. 2 c. 3 d. 0 - b. 2 Generally, in a cycloaddition reaction, does the LUMO of the dienophile interact with the HOMO of the diene? - According to frontier orbital theory, in a cycloaddition reaction, the LUMO of the dienophile interacts with the HOMO of the diene. The electron density flows from a filled orbital (HOMO) of the electron-rich diene into an empty orbital (LUMO) of the electron-poor dienophile. When these frontier
orbitals are aligned, the phases of the MOs must overlap in order to have constructive interference. This requirement is called conservation of orbital symmetry. Pericyclic Reactions: Do NOT involve ___ or ___ intermediates - Ionic or Radical How many sigma and pi bonds are broken and formed in a Cycloaddition Reaction? - In a cycloaddition reaction there are 2 sigma bonds formed in each pericyclic reaction and there are 2 pi bonds broken each time. What is not one feature all pericyclic reactions share? a. Concerted mechanism b. Closed loop ring movement c. Cyclic transition state d. Radical intermediates - d. Radical intermediates Describe the thermodynamic control that pericyclic reaction posses at low temperatures. - At low temperatures, competing reaction pathways are irreversible, this is due to the fact that there is not energy convert back to reactants. This lack of energy also causes 1,2 addition to be favored. This pathways has a lower activation energy. Larger alkyl groups increase boiling point due to ___________. - Increased London dispersion forces Sharpless Asymmetric Epoxidation uses a chiral center to achieve __________ epoxidation of allylic alcohols. - enantioselective When alkenes are less substituted products form more rapidly because of? - The products form faster because of proximity effect which is referring to the nucleophile oxygen atom can most easily access the electron-deficient that is closest to it. Explain if ethers are soluble in water. - Ethers are less polar than alcohols making alcohols more soluble in water than ethers because they can form hydrogen bonds with water as hydrogen bond donors and
B.) Covalent, Ionic C.)Conjugated, Isolated D.)Ionic, Covalent E.)Molecular Covalent - C.)Conjugated, Isolated Thiols used to be called _______. - Mercaptan What is Conjugated diene? - Conjugated diene is a system of overlapping p orbitals.Two pi bonds form 4 overlapping p orbitals.Conjugated diene has special properties and reactivity. Explain the proximity effect at high and low temperatures. - At low temperatures, the competing reaction pathways are irreversible. Also, 1,2-addition occurs more rapidly with not enough energy to convert the 1,2-adduct back to an allylic carbocation. At high temperatures competing pathways are reversible and there is enough energy to lose a Leaving group and reform an allylic carbocation. The condition __________ orders two molecules of ethylene to undergo a cycloaddition reaction to give cyclobutane. - photochemical excitation Pericyclic reactions do NOT involve ________ or ________ intermediates. - ionic, radical In a Diels-Alder reaction mechanism, the electron movement arrows (forming the cyclic ring) can move either/both __________ and __________. In either instance, the mechanism arrows are still correct. - clockwise and counterclockwise A reaction that consists of a dienophile with an electron-withdrawing group leads to a reaction with __________. a. A slower reaction b. A faster reaction c. A lower yield d. A higher yield e. Both A and C
f. Both B and D - f. Both B and D What are the 2 frontier orbitals that have been discussed throughout the course of chapter 16? What are their acronyms? What do the acronyms stand for? - The 2 frontier orbitals that were discussed in chapter 16 were HOMO and LUMO. The HOMO acronym stands for "highest occupied molecular orbital," while the LUMO acronym stands for "lowest unoccupied molecular orbital." If a diene or dienophile is symmetrical, what could one assume about the number of regiochemical outcomes? Briefly explain. - If a diene or dienophile is symmetrical, one could assume that there is only one regiochemical outcome. With one half of the combining cyclic ring being symmetrical within itself, only one regiochemical outcome is physically possible. In a reaction with a cis dienophile, why (name at least one reason) is an endo product the more highly favored product? - With a cis dienophile, the endo product is highly favored (compared to the exo product) and it is sometimes the exclusive product in a number of reactions. This phenomenon is primarily due to the transition state of each possible outcome. In the transition state leading to an endo product, there is a favorable interaction between the developing pi bond and the electron-withdrawing substituents. In the transition state leading to an exo product, there isn't a favorable reaction because the developing pi bond and the substituents are too far apart from one another. Therefore, this also leads to the outcome by which an endo transition state is lower in energy than that of the exo transition state. Pigeons can see very well in bright light but are blind at night. This means that pigeon eyes contain _________. - Cones only In the [4+4] cycloaddition reaction between two molecules of 1,3-butadiene to form cis-1,5- cyclooctadiene, the (A) of one 1,3-butadiene molecule interacts with the (B) of a second 1,3-butadiene molecule. - (A) excited state HOMO, (B) ground state LUMO In a cycloaddition reaction between two 1,3-butadiene molecules, the overlap of the ground state HOMO of one 1,3-butadiene with the ground state LUMO of the other is symmetry forbidden. A [4+4] cycloaddition can only be performed under photochemical excitation where the excited state HOMO of
The boiling point of ethyl alcohol is much higher that that of dimeyhyl ether though both have the same molecular weight. Why? - Alcohols have much higher boiling points than the comparable alkanes or related ethers because of molecules of alcohols can interact through hydrogen bonding while those of alkanes and ethers cannot. What type of diene is a system of overlapping p orbitals? a. Isolated diene b. Conjugated diene c. Double diene d. Cumulated diene - b. Conjugated diene Why do epoxides undergo reactions? - To open the ring to alleviate ring strain. ________ double bonds are more stable than _______ double bonds. - Conjugated, isolated What do all three types of pericyclic reactions have in common? - All three are concerted processes, they are a ring of electrons moving around a closed loop, all have a cyclic transition state, and the polarity of the solvents has very little impact on the rates and yield suggesting the transition state has very little if any partial charge.
