Organic Chemistry Final Exam

True or False: The chemical personality and therefore reactions of alkynes are very similar to the chemical personality and reactions of alkanes.

- False

What is the molecular orbital theory?

- the electron density in molecules can be described mathematically by adding the wave functions of all the atomic orbitals for all the atoms in the entire molecule

What is the Valence Bond Theory?

- The wave functions for the valence atomic orbitals on each atom can be added together (hybridized) first, before looking for overlap with orbitals from other atoms

What are constitutional isomers?

- molecules with the same molecular formula but different connectivities between atoms

True or False: The chemical personality and therefore reactions of alkynes are very similar to the chemical personality and reactions of alkenes.

- True

During the process of tautomerization, the "keto" form is more stable than the "enol" form because...

- C=O pi bonds are stronger than C=C pi bonds

Is NaNH2 a strong base of acid?

- a wicked strong base

What is the big deal about the NaNH2 reaction and what type of reaction is it?

- big deal: made a C-C bond

- Sn2 reaction

Is the enol or keto form of a molecule more stable, and why?

- keto form is more stable because a C=O is stronger than a C=C bond

When alkynes react with JUST BH3 what do you get?

- you get 2 different products one Markovnikov and the other non-Markovnikov

When an alkyne reacts with (sia)2BH what do you get?

- you get a C=O to the least substituted carbon

- non-Markovnikov

When an alkyne reacts in the presence of mercury what do you get?

- you get a C=O to the most substituted carbon

- Markovnikov

When using Lindlar's catalyst, internal alkynes are reduced to give the following type of alkene:

- Z (cis)

When using dissolving metal reduction, internal alkynes are reduced to the following the of alkene:

- E (trans)

Sodium metal gives up an electron in the alkyne reduction because

- elemental sodium has a single electron in its outer shell, so losing one electron gives a filled outer shell

- natural unstable and wants to become stable

What are the steps in the free radical chain mechanism for the halogenation of alkanes?

1. Initiation

2. Propagation

3. Termination

Which of the following are considered to be relatively weak bonds.

1. The Cl-Cl bond of Cl2

2. The central C-C bond of ethane

3. The Br-Br bond of Br2

4. The central O-O bond in hydrogen peroxides

- 1,3,4

Carbon radicals are analogous to carbocations. For that reason, the order of carbon radical stability is (ranked from most to least stable carbon radical):

- Tertiary > Secondary > Primary > Methyl

If a radical must exist, what is the best way to make it stable?

- have it distributed over many atoms through resonance, inductive effects, & hyper-conjugation

While Lindlar's catalyst gives a cis alkene, which reaction give a trans alkene?

- chemical reduction with sodium & ammonia gives a trans alkene

What typically happens in an SN2 mechanism?

- there is a leaving group and when a nucleophile reacts with it, the leaving group departs and inverts the original position of everything else

True or False: When HBR is added to an alkene in the presence of peroxides and heat the reaction intermediate is a radical.

- True

True or False: The reaction mechanism for the SN2 reaction involves an intermediate with 5 bonds to carbon.

- False

True or False: The E2 reaction mechanism requires a geometry in which the base and the leaving group line up in an antiperiplanar transition state geometry

- True

What are the 4 different mechanisms that are possible when a haloalkane reacts with a nucleophile/base?

- Sn2

- E2

- Sn1/E1

What are the leaving groups we need to recognize for this class?

- I

- Br

- Cl

- NOT F

What kind of intermediate does the Sn1/E1 reactions have?

- carbocation

How do primary haloalkanes react with nucleophiles/bases?

- they will go through a Sn2 reaction unless tBuO- is used then it will be an E2 reaction

Axial or Equatorial: Cyclohexane & Sn2 reaction

- axial

- allows nucleophile to approach from the back w/o steric hinderance

Axial or Equatorial: Cyclohexane & E2 reaction

- axial

- gives anti- periplanar configuration

Which mechanism will this reaction undergo: A primary haloalkane reacting with NaOH

- Sn2

Which mechanism will this reaction undergo: A secondary haloalkane reacting with NaOH

- E2

Which mechanism will this reaction undergo: A tertiary haloalkane reacting with methanol (CH3OH)

- Sn1/E1

What are the three strong bases and what is a big clue for them?

- R-C=C-

- R-O-

- H-O-

- all of the strong bases are deprotonated

What are the three very weak bases and what is a big clue for them?

- R-CO2H

- R-O-H

- H2O

- all the very weak bases are protonated

Alcohols react with Li, Na, or K to give H2 along with Li+, Na+, or K+ and...

- an alkoxide

Alcohol reaction generally involve converting the OH into...

- a leaving group

In the acid-catalyzed dehydration reaction of alcohols, the products are an alkene and...

- water

In most. stable molecules, all the atoms will have ______ valence shells.

- filled

What is the most important question in chemistry?

Where are the electrons?

What attracts the majority of electron density in a bond?

- according to Linus Pauling, the more electronegative atoms

Neutral boron takes part in ____ bond(s) and has ____ non-bonded pairs of electrons.

- 3

- 0

Neutral bromine takes part in ____ bond(s) and has ____ non-bonded pairs of electrons.

- 1

- 3

A carbon atom with 1 non-bonded pair of electrons and 3 bonds has a ____ formal charge.

- -1

An Oxygen atom with 1 non-bonded pair of electrons and 3 bonds has a ____ formal charge.

- +1

True or False: A sigma bond occurs when the majority of the electron density is found on the bond axis.

- True

True or False: When drawing resonance contributing structures, you should move pi bonds (one bond of a double or triple bond) and lone pair electrons, not atom nuclei or sigma bonds.

- True

True or False: For organic chemistry, it is best to think of electron density as particles, described by Newton's laws.

- False

True or False: Resonance contributing structures do not represent equilibrating structures, rather the hybrid (blending) of them is the true molecular representation.

- True

True or False: An sp3 hybridized carbon atom has only one major hybridized orbital.

- False

True or False: For unequal resonance contributing structures: full octets are favored, more covalent bonds are favored, fewer charges are favored, and a negative charge on more electronegative atoms (also positive charge on less electronegative atoms) are favored.

- True

True or False: Resonance contributing structures are used when more than one structure are required to describe accurately how the electrons and charges are distributed in a molecule.

- True

True or False: When drawing resonance contributing structures you generally move atom nuclei and sigma bonds.

- False

True or False: A pi bond occurs when the majority of the electron density is found on the bond axis.

- False

True or False: An sp3 hybridized carbon atom has only two major hybridized orbitals, arranged in a bent geometry.

- False

True or False: Equivalent resonance contributing structures make equal contributions to the resonance hybrid.

- True

True or False: An sp3 hybridized carbon atom has four major hybridized orbitals, arranged in a tetrahedral geometry.

- True

True or False: Sigma bonds rotate at room temperature.

- True

True or False: Pi bonds rotate at room temperature.

- False

Briefly describe torsional strain.

- Torsional strain is present when H atoms are very close together which usually occurs in an eclipsed formation

Briefly describe steric strain.

- Steric strain is when atoms have the potential & do "crunch" into each other. To avoid steric strain, you want to have an anti conformation with two methyl groups across from each other and not next to each other

Briefly describe angle strain.

- Angle strain is present at any moment any bond angle of an sp3 C atom is different than the ideal of 109.5 degrees; can be caused by ring structures

Which formation is more stable for longer chain alkanes?

They exist primarily in the more stable zigzag conformation b/c it is all staggered AND minimizes steric strain

Three (or more) atom "pi-ways" are the situation resonance ______ structures are usually trying to describe. For pi bonding and therefore pi delocalization to occur over more than two atoms, parallel and overlapping ________ orbitals are needed on ALL of the adjacent atoms involved. As a result, all of the atoms involved in pi-ways are usually _______ hybridized, and NEVER ________ hybridized.

- contributing

- 2p

- sp2

- sp3

True or False: Resonance contributing structures do not represent equilibrating structures, rather the hybrid (blending) of them is the true molecular representation.

- True

True or False: A sigma bond occurs when the majority of the electron density is found on the bond axis.

- True

True or False: An sp2 hybridized carbon atom has three hybridized orbitals, arranged in a trigonal planar geometry.

- True

True or False: An sp3 hybridized carbon atom has 4 hybridized orbitals, arranged in a tetrahedral geometry.

- True

True or False: For organic chemistry, it is best to think of electron density as waves, described by wave equations.

- True

True or False: For organic chemistry, it is best to think of electron density as particles, described by Newton's laws.

- False

True or False: An sp hybridized carbon atom has two hybridized orbitals in a linear geometry.

- True

Cyclobutane is puckered to minimize _____ and _____ strain.

- Torsional & angle

Cyclobutane is considerably more _____ and ____ strain compared to cyclohexane.

- Torsional & angle

______ strain is the term used to explain that eclipsed conformations of ethane are less stable than staggered conformations. For butane, the most stable conformation is the staggered, anti conformation because this conformation minimizes ____ strain between the methyl groups.

- Torsional & Steric

Large groups on cyclohexane molecules prefer to be ________ primarily because of ________ strain. Another name for this kind of strain is a(n) __________ interaction.

- Equatorial

- Steric

- Diaxial

When drawing the direction of the dipole bond, which way does the arrow point?

- The arrow should point toward the more electronegative atom

How do you know which contributing structure makes the largest contribution? List in order of top priority.

- More atoms w/ filled valence shells

- More total # of bonds

- Fewer charges overall

- (-) on more electronegative atoms or (+) on less electronegative atoms

When we have a triple bond, what is the hybridization of the bottom bond, the middle, & top?

- For a triple bond, 2 bonds will have 2p hybridization & the other on will be sp (bottom bond)

When we have a double bond, what is the hybridization of the bonds?

- 1 bond will be 2p while the other will be sp2

What is the fact about alkane branching and boiling points?

- Branch decreases boiling point b/c dispersion forces (attraction b/t temporary partial charges on adjacent molecules)

How do you properly assign whether a chiral molecule/ atom is R or S

1. Assign atomic # priorities of each group; ranking them 1-4 (1st point of difference wins)

2. Position molecules so you are looking down the C→4 bond

3. Count the remaining 3 groups in order

- If clockwise (R)

- If counterclockwise (S)

What does the "L" designation of amino acids refer to?

- the fact that all of the common chiral amino acids have chirality that is structurally related to L-glyceraldehyde

When you're analyzing relative acid strengths of two different acids that deprotonate to make anion conjugate bases, what exactly should you analyze?

- structures of the anion conjugate bases

True or False: For reactions, the "motive" is present if products are more stable (lower in energy) than starting materials.

True