Chapter 2: Molecular Representations

Flashcards covering 2.1 to 2.13 topics from the lecture notes on molecular representations, bond-line structures, functional groups, formal charges, resonance, and 3D notation.

What are the two common molecular representations discussed in 2.1?

Dash formula (bond-line) and condensed formulas.

In a bond-line structure, what does each corner or endpoint represent?

A carbon atom.

Are hydrogen atoms drawn on bond-line structures?

No; they are assumed to complete the octet.

What is the zigzag format used for in bond-line drawings?

To depict sp3/sp2 hybridized carbons with approximate bond angles in straight chains.

What is the 'cardinal rule' for carbon valence in bond-line structures?

Never draw more than four bonds to a carbon (octet rule).

Rule 1 for drawing bond-line structures (2.2)?

Sp2 and sp3 hybridized atoms in a straight chain should be drawn in zigzag format.

Rule 2 for drawing bond-line structures (2.2)?

When drawing double bonds, draw all bonds as far apart as possible.

Rule 3 for drawing bond-line structures (2.2)?

When drawing single bonds, the direction in which the bonds are drawn is irrelevant.

Rule 4 for drawing bond-line structures (2.2)?

All heteroatoms must be drawn, as well as the H atoms attached to them.

Rule 5 for drawing bond-line structures (2.2)?

Never draw more than four bonds to a carbon atom (octet rule).

In skeletal (bond-line) structures, where are hydrogens shown?

They are not shown; there are enough to complete the octet.

Why are bond-line structures useful for reactions?

They make it easier to see bonds formed/broken and functional group transformations.

What functional group does R-OH represent?

Alcohol.

What functional group does R-O-R represent?

Ether.

What functional group does R-CHO represent?

Aldehyde.

What functional group does R-CO-R represent?

Ketone.

What functional group does R-COOH (R-CO2H) represent?

Carboxylic acid.

What functional group does R-SH represent?

Thiol.

What functional group does R-S-R represent?

Sulfide.

What functional group is an aromatic ring (arenes) like methylbenzene?

Aromatic (arene).

What functional group is represented by an amide?

Amide.

What functional group is represented by an amine?

Amine.

What functional group is represented by an ester?

Ester.

What functional group is represented by an acetyl chloride example?

Acyl halide.

What functional group is represented by acetic anhydride?

Anhydride.

How many bonds does a carbon atom typically have when it has no formal charge?

Four bonds.

What is a carbocation's typical bonding pattern?

Three bonds (and one empty orbital).

What is a carbanion's bonding pattern?

Three bonds plus a lone pair.

What must be drawn when using resonance forms to ensure validity?

Formal charges.

What do curved arrows depict in resonance?

Electron movement and delocalization across pi bonds and lone pairs.

What is the rule about delocalizing sigma bonds when using curved arrows?

Never show a sigma (single) bond as being delocalized.

What is the octet rule constraint for second-row elements in resonance drawings?

Never exceed an octet (8 electrons for B, C, N, O, F in the valence shell).

What is a resonance hybrid?

The average of all significant resonance contributors; the actual structure is a hybrid.

Name Pattern #1 in resonance pattern recognition.

Allylic lone pair.

Name Pattern #2 in resonance pattern recognition.

Allylic carbocation.

Name Pattern #3 in resonance pattern recognition.

Lone pair adjacent to a carbocation.

Name Pattern #4 in resonance pattern recognition.

A pi bond between two atoms of differing electronegativity.

Name Pattern #5 in resonance pattern recognition.

Conjugated pi bonds in a ring.

What must a lone pair be adjacent to in order to be delocalized?

An atom with an unhybridized p orbital.

If a nitrogen lone pair participates in resonance, what is nitrogen's hybridization?

sp2.

What is the 3D notation used to show orientation in bond-line structures?

Dashed and solid wedged lines.

Why do resonance structures often require curved arrows?

To show the movement of electrons between atoms or orbitals and illustrate delocalization.