Organic Structure, Hybridization, Resonance, Aromaticity

What must be true for a molecule to be aromatic?

it is cyclic, it is fully conjugated (no sp³ carbons), it is planar, and follows huckels rule

What is huckels rule?

in order for a molecule to be aromatic, the total # of pi electrons in the molecule must be equal to 4n+2 where n is a whole, positive integer (including 0)

Formal charge =

Z - 1/2S - U (where Z = element group number, S = number of shared electrons, U= = number unshared electrons)

All individual formal charges should add to BLANK

Total charge on molecule

How to determine the hybridization of an atom?

Count number of attached atoms, and number of lone electron pairs

If an atom has 4 atoms/lone pairs, what is the hybridization?

sp³

If an atom has 3 atoms/lone pairs, what is the hybridization?

sp²

If an atom has 2 atoms/lone pairs, what is the hybridization?

sp

When does electron counting for hybridization not apply?

when a lone pair is next to a pi bond

In each pi-bond, how many electrons are pi electrons?

2

If a carbon with a pi bond is adjacent to a carbon with a lone pair of electrons

the lone pair are pi electrons

If an atom has two lone pairs, is sp² hybridized, and is adjacent to a pi bond

one lone pair will be pi electrons and the other will be hybrid

If a lone pair of electrons on an sp² hybridized atom is adjacent to pi bonding

the pair are pi electrons

what is the order of stability for carbocations?

MOST STABLE: allylic > 3^o > 2^o > 1^o > vinyl

an allylic carbocation

tertiary carbocation

secondary carbocation

primary carbocation

vinyl carbocation

Benzyllic carbocations are more stable than

allylic carbocations

More strain in a cyclic molecule will cause a greater

heat of combustion

If the heat of combustion of a molecule is lower, it is

more stable

a positive charge is most stable on the BLANK electronegative atom

least

a negative charge is most stable on the BLANK electronegative atom

most

more covalent character means a molecule is

more stable

charge separation in a molecule makes it

less stable

What are the three main type of resonance transformations?

neutral, charged, allylic

in neutral resonance transformations

electrons from a double bond move to a bonded atom, creating opposite positive and negative charges

In charged resonance transformations

pi electrons move to a charged atom, creating a charge on the oppositely bonded atom (in one electron move, an extra can move th charge further)

Allylic resonance

When a lone pair creates a pi bond and the adjacent pre-existing pi bond is forced into a lone pair on the opposing atom