Organic Chemistry: Electronic Structure + Bonding Flashcards

What is formal charge and what is the formula to calculate it?

Formal charge is the difference between the valence electrons of an atom and the number it "owns" when bonded to another atom. Formula: Formal charge = # valence electrons - (# lone pair electrons + # bonds)

How many bonds does neutral nitrogen form and what happens when nitrogen is charged?

Neutral nitrogen forms 3 bonds with 1 lone pair. When charged, nitrogen can form 4 bonds (positive charge) or 2 bonds (negative charge).

What happens when carbon does not form four bonds?

If carbon does not form four bonds, it has a charge (or it is a radical).

How many bonds do hydrogen and halogens typically form, and what happens when they don't follow this pattern?

Hydrogen and halogens typically form 1 bond (halogens have 3 lone pairs). If they don't form one bond, they have a charge (or are radicals).

What is the first step in drawing Lewis structures?

Determine the total number of valence electrons (1 for H, 4 for C, 5 for N, 6 for O). If the molecule is charged, add 1 electron for every negative charge and subtract 1 electron for every positive charge.

What is the second step in drawing Lewis structures?

Distribute atoms, remembering that C forms 4 bonds, O forms 2 bonds, H forms 1 bond, and N forms 3 bonds. Put the fewer atom(s) in the middle.

What are the remaining steps for drawing Lewis structures after distributing atoms?

1. Use total valence electrons to form bonds and fill octets with lone pairs 2. Third row elements can exceed octet but never second row elements 3. Make double or triple bonds to satisfy octet if you run out of valence electrons 4. Assign formal charges where applicable

What are Kekule structures?

Like Lewis structures except lone pairs are normally omitted.

What are condensed structures?

Simplified structures created by omitting some or all covalent bonds and listing atoms bonded to a particular carbon (or N, O) next to it. A subscript is used if there is more than one particular atom.

What are skeletal (bond-line) structures and what is the key rule about what disappears?

Show carbon-carbon bonds as lines but do not show the carbons or hydrogens bonded to carbons. Key rule: "only C and H disappear". Note: hydrogens bonded to heteroatoms (O, N, S, etc.) must be shown.

What is Rule 1 for drawing organic molecules in skeletal structures?

sp² and sp³ hybridized atoms in a straight chain should be drawn in zigzag format.

What is Rule 2 for drawing organic molecules with double bonds?

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

What are Rules 3, 4, and 5 for drawing organic molecules?

Rule 3: Direction of single bonds is irrelevant Rule 4: All heteroatoms (other than C and H) must be drawn, as well as H atoms attached to them Rule 5: Cardinal rule - never draw more than four bonds to a carbon atom (recall octet rule)

What is the functional group for alcohols and how do you identify them?

Functional group is R—OH. Look for OH groups in the structure.

What is the functional group for amines and how do you identify them?

Functional group is R—NH₂. Look for nitrogen atoms in the structure.

What are the functional groups for aldehydes and ketones, and how do you distinguish them?

Aldehyde: functional group has H attached to C=O (at end of chain). Ketone: functional group has CH₃ or other carbon groups attached to C=O (in middle of chain).

What is the functional group for carboxylic acids?

Functional group is O=C-O-H (carboxyl group).

What is the functional group for esters?

Functional group is O=C-O-C (carbonyl connected to oxygen, which connects to another carbon).

What is the functional group for amides?

Functional group is O=C-N (carbonyl connected to nitrogen).

What is the functional group for ethers?

Alkyl groups bound to an oxygen (R-O-R).

What is an atomic orbital and what percentage defines the region?

An atomic orbital is a region of space around the nucleus where an electron is most likely to be found (>90% probability).

What is a node in atomic orbital theory?

A node is a region where there is zero chance to find an electron.

What important property do electrons have according to orbital theory?

Electrons have both particle-like and wave-like properties.

What is important about the lobes of p atomic orbitals?

The lobes of p atomic orbitals have opposite phases.

What does molecular orbital (MO) theory complement and what does it consider?

MO theory complements the Lewis model of bonding by considering the wavelike properties of electrons.

How are covalent bonds formed according to MO theory?

Covalent bonds are formed when atomic orbitals combine to make molecular orbitals.

What is a sigma bond (σ)?

A sigma bond is a covalent bond formed when two s orbitals overlap.

What causes atomic orbitals to come together and what happens to energy?

Attractive forces between positively charged nuclei and negatively charged electrons cause orbitals to come together, and energy decreases.

What happens when atomic orbitals get too close to each other?

Repulsive forces between the two positively charged nuclei start dominating, and energy starts to increase.

What is the conservation rule for molecular orbitals?

Orbitals are conserved: # Molecular Orbitals = # Atomic Orbitals combined.

When do bonds occur according to MO theory and what type of interference is required?

Bonds occur when atomic orbitals overlap. Only constructive interference (same phase) results in a bond.

What is the result of constructive combination of two s atomic orbitals?

Constructive combination of two s atomic orbitals is called sigma bonding.

What happens when waves with opposite phases overlap?

Waves with opposite phases overlap destructively, canceling each other and forming a node. This is called anti-bonding.

What happens when two atomic orbitals overlap in terms of energy levels?

When two atomic orbitals overlap, two molecular orbitals are formed - one lower in energy (bonding) and another higher in energy (anti-bonding).

Where do electrons go when atomic orbitals overlap and why?

Electrons go into the bonding MO rather than the antibonding MO to achieve a lower energy state.

Why does the antibonding MO have higher energy?

The antibonding MO has higher energy because it has one node.

What is the formula for bond order?

Bond order = 1/2(# bonding electrons - # antibonding electrons)

What forms a pi bond or pi* (pi star)?

Side-to-side overlap of two parallel p orbitals forms a pi bond or a pi*.

What is the difference between pi bond formation and pi* formation?

Side-to-side overlap of two in-phase p orbitals forms a pi bond. Side-to-side overlap of two out-of-phase p orbitals forms a pi* antibonding MO.