Chem 215-1: Quiz 1

When is a resonance structure lower in energy?

1. More atoms with a completed octet

2. Fewer atoms nonzero formal change

3. A -1 formal charge appearing on more electronegative atom (and +1 on less electronegative)

Why are resonance structures stabilized?

Delocalization of electrons because electrons are less confined

When is a structure highly stabilized?

When there are more equivalent resonance structures

What do nonequivalent resonance structure do?

They have a small contribution to the hybrid

What features indicate that another resonance structure exists? (not ranked)

1. Lone pair on an atom adjacent to a multiple bond

2. Atom lacking an octet adjacent to a multiple bond

3. Atom with a lone pair adjacent to an atom lacking an octet

4. Polar multiple bond (can lead to no octet and formal charges on 2 atoms)

5. Ring of alternating single and multiple bonds (benzene)

Just memorize

What is this?

Arene/aromatic compound

What is this?

Thiol

What is this?

Nitrile

What is this?

Ether

What is this?

Ketone

What is this?

Acetal

What is this?

Aldehyde

What is this?

Alkyl halide

What is this?

Hemiacetal

What is this?

Carboxylic acid

What is this?

Alcohol

What is this?

Epoxide

What is this?

Ester

What is this?

Phenol

What is this?

Amine

What is this?

Amide

What is this?

Alkene

What is this?

Alkyne

In dash wedge notation, which one is towards you?

Wedge

Do alkanes contain functional groups?

No

What are the basic alkanes?

Straight-chain / linear alkanes

• No branches

What are the prefixes for nomenclature?

Meth, eth, prop, but, pent, hex, hept, oct, non, dec

What are substituted alkanes?

If a hydrogen atom of an alkane is replaced by another atom or group of atoms → substituted

What are the prefixes for halo substituents and NO₂ substituents?

Fluoro, chloro, bromo, iodo, nitro

What are the prefixes for substituents?

di, tri, tetra, penta, hexa, hepta, octa, nona, deca

How to determine if a ring is a root or substituent?

Compare number of carbons in ring vs in longest continuous chain (if in ring, NOT in chain)

• Called cycloalkane if root (ex. cyclopropane)

• Called cycloalkyl if substituent (ex. cyclopropyl)

What is isopropyl?

End of carbon chain with two methyls off of it

• Iso___yl refers to a chain of carbons where a methyl exists on C-2 (looks like carbon chain with 2 methyls off it)

What is tert-butyl

Carbon chain with 3 methyl groups coming off it

• All tert means is that the terminal carbon is attached to 3 other carbons (3 methyl groups)

ADD VSEPR HERE

When atoms are connected by a multiple bond, are they in the same plane or different?

Those atoms and atoms to which they are directly bonded prefer to lie in same plane

Why does cis-1,2-dichoroethene have a higher boiling point than its trans counterpart?

Due to the dipole that’s formed

How do you determine if a molecule has two distinct configurations about the double bond?

See if there are two different atoms/groups attached to each double bonded C (on C has 2 different groups)

What happens to the bond length as hybridization goes from sp³ to sp² to sp?

Become shorter (+ stronger)

• Has more s character, so bond length decreases because s orbital is closer to the nucleus than the p orbital

What happens to the effective electronegativity as hybridization goes from sp³ to sp² to sp?

Increases (more polar portions of the molecule)

What does a node represent?

Surfaces where there is a zero probability of finding an electron

What are the relative energy levels of bonding, antibonding and nonbonding MOs?

• Bonding is significantly lower in energy than contributing AOs

• Antibonding is significantly higher in energy than its contributing AOs

• Non-bonding has the same energy as contributing AOs

What are the HOMO and LUMO?

HOMO = highest energy w/ an electron, LUMO = lowest empty

ADD Last two slides from lecture 4, about hybrid atomic orbitals