Orgo 15.1-15.5

Double bonds that aere separated by two or more single bonds are called __.

When a molecule has two isolated double bonds, the heat of hydrogenation is __. 

For conjugated dienes, the heat of hydrogenation is __.

What happens if two double bonds are even closer togeter than in the conjugated case? These are called __.

The heat of hydrogenation of these is __, thus making them __.

When a molecule is more stable than another, that extra energy is __, also called __.

The pi bonds in 1,3-dienes are__.

Why are pi bonds shorter?

The electrons in the double bonds are __ over the entire molecule, creating some pi overlap and pi bonding in the C2-C3 bond. The length of this bond is __ between the normal length of a single bond and that of a double bond.

All four carbon atoms of buta-1,3-diene are __.

In __, the lobes that overlap in the bonding region betewen the nuclei are in phase; they have the same sign. This is __.

In the pi __, lobes of opposite phase overlap in the bodning region called __, thus cancelling of the wave function in the bonding region. Midway between the nuclei, this antibonding MO has a __: a region of zero electron density where positive and negative cancel out.

Electrons have lower energy in the __ than in the original p orbitals, and higher energy in the __. Stable molecules tend to have __ and __.

The number of MOs is always the same as __. These MOs have energies that are symmetrically distributed __ and __ the energy of the starting p orbitals. Half are __ and half are __.

Why is the lowest-energy orbital exceptionally stable?

The second molecular orbital (pi2) of butadiene has one __ in the center of the molecule. THis MO represents the classic picture. What is the classic picture of a diene?

The pi orbital has __ and __, so we expect it to be a __. It is not as strongly bonding nor as low in energy as the __. Adding and subtracting bonding and antibonding interactions is not a reliable method for calculating energies of molecular orbitals, but it is useful for predicting whether a given orbital is bonding or antibonding and for __.

The third butadiene MO (pi3*) has __. There is a bonding interaction at the C2-C3 bond, and there are two antibonding interactions one between C1 and C2 and the other between C3 and C4.  This is an __ and it is __.

The fourth, and last, MO (pi4*) of buta-1,3-diene has __ and is totally __. This MO has __ and is unoccupied in the molecule's ground state. This __ is typpical: For most systems, the highest-energy MO has antibonding interactions between all pairs of adjacent atoms.

Each MO can accommodate __, and the __ are filled first. Therefore, the four pi electrons go into __ and __.

The partial double bond character between C2 and C3 in buta-1,3-diene explains why the molecule is most stable in the __. There are actually __ that allow overlap between C2 and C3. These conformation sarise by __ about the C2-C3 bond, and they are considered single-bond analogues of trans and cis isomers about a double bond. Thus, they are named __ and __.

The __ is more stablethan the __.

What are some common intermediates of conjugated compounds? Describe how they are the intermediate.

What is the allyl group?

When allyl bromide (CH2=Ch-CH2Br) is heated with a good ionizing solvent, it ionizes to the __, an allyl group with a positive charge. More-substituted analogues are called __ which are stabilized by __ with the adjacent double bond, which delocalizes the positive charge over two carbon atoms.

Because of its resonance stabilization the primary allyl cation is __ a simple secondary carbocation. Most subbed allylic cations have at least one __ bearing part of the positive charge. They are about as stable as __.

What is the order of stability of carboncations?

__ usually involve allylic cations as intermediates. Unlike simple carbocations, an allylic cation can react with a __ at __.

The first product results from electrophilic addition across a double bond, called __. 

In the second product, the proton and the bromide ion add at the ends of the conjugated system to carbon atoms with a __, called __.

In these additions, the __ is the electrophile, adding to the alkene to give the __, which usually occurs through __.

Attack of the bromide (or other) in an addition reaction at the secondary carbon gives __; attack at the primary carbon gives __.

What is the mechanism for 1,2- and 1,4- addition of a conjugated diene?

The key to formation of these two products is the presence of __.