Chapter 2: Molecular Representation

How many ways are there to represent molecules?

Many (Lewis structures, condensed structure, partially condensed structure, and molecular formula)

Which structure gives the most information?

Lewis structure

Count the number of carbon and hydrogen atoms in the structures below

How many carbon and hydrogen atoms are in the following

molecule?

C₁₅H₂₃

Can single bonds rotate?

Yes so be aware of that

Give alternative bond-line structures for the molecule below

Draw bond-line representations for 3 possible isomers given the

formula: C5H9ClO

Draw bond-line representations for the following Lewis structures

What are functional groups?

When certain atoms are bonded together in specific arrangements, they undergo specific chemical reactions

Identify the functional group

alkyl halide

Identify the functional group

alkene

Identify the functional group

alkyne

Identify the functional group

alcohol

Identify the functional group

ketone

Identify the functional group

aldehyde

Identify thr fiunctional group

carboxylic acid

Identify the functional group

acyl halide

Identify the functional group

ether

Identify the functional group

thiol

Identify the functional group

sulfide

Identify the functional group

aromatic

Identify the functional group

anhydride

Identify the functional group

ester

Identify the functional group

amide

Identify the functional group

amine

Name the functional groups

1. Alkane

2. Alkene

3. Alkyne

4. Alkyl halide

5. Ketone

6. Amide

7. Phenol

8. Sulfide

What are carbocations

a positive formal charge on carbon

What is a carboanion?

Is a negative formal charge on carbon

What does a formal charge on nitrogen look like?

What does a formal charge on oxygen look like?

Which of the indicated atoms has only one lone pair?

find the answer

How do we show a 3D molecule on a 2D piece of paper ?

dashed and solid wedges

What are some of the ways to show 3D structures?

What is resonance?

when all carbons have un hybridized p orbitals

• we used brackets to indicate both resonance contributors exist simultaneously

Does resonance make a molecule more or less stable?

MORE stable

Why does resonance make a molecule more stable?

Resonance increases stability by delocalizing electrons and charge.

• Electron delocalization: electrons are spread over a larger area, reducing electron–electron repulsion and allowing interaction with multiple nuclei

• Charge delocalization: charge is distributed over multiple atoms, making partial charges more stable than a single full charge

What do curved arrows represent in organic chemistry?

Curved arrows show the movement of electrons, usually electron pairs

• The arrow starts where the electrons are currently located

• The arrow ends where the electrons will be after the movement

What are the rules for using curved arrows to show resonance?

1. Avoid breaking a single bond, single bonds can break but not in resonance

2. Never exceed an octet for 2nd row elements (B, C, N, O, F)

3. 2nd row elements (B, C, N, O, F) will rarely but sometimes have LESS than an octet

Determine which of the three main rules of drawing a curved arrows the following actions violate, if any rules are broken

Which of the following represent correct curved arrow notation for drawing resonance structures?

Figure it out

There a 5 main bonding patterns in which resonance occurs, what are those 5 patterns?

1. Allylic lone pairs

2. Allylic positive charge

3. Lone pair of electrons adjacent to a positive charge

4. A pi bond between two atoms with different electronegativities

5. Conjugated pi bonds in a ring

What does vinyl mean?

directly bonded to C=C double bond

What does allyl mean?

one atom away from a C=C double bond

An example of vinyl and allyl in a compound

If there are multiple double bonds (conjugated), then multiple contributors are possible. Show the resonance contributors and curved arrows below

How many curved arrows are needed in common resonance patterns?

allylic lone pair = 2 arrows

allylic positive charge=1 arrow

lone pair next to + charge = 1 arrow

Nitro group = 2 arrows (to preserve octet)

Aromatic ring (benzene) = 3 arrows

Why can’t we use one curved arrow to remove the positive charge in the nitro group?

because one curved arrow would give nitrogen more than 8 electrons and violate the octet rule

What happens when a π bond in between atoms of different electronegativity?

The π electrons shift toward the more electronegative atom using one curved arrow, creating a resonance structure with:

• a negative charge on the more electronegative atom

• a positive charge on the less electronegative atom

How do you draw resonance for conjugated π bonds in a ring?

1. Every atom must have a p orbital (sp² or sp)

2. π electrons are delocalized around the ring

3. Move all π bonds together using three curved arrows

4. Arrows can go clockwise or counterclockwise

finish this answer

finish this answer

How is the stability of resonance contributors assessed?

1. Formal charge generally decreases stability, especially a +1 charge on an electronegative atom or -1 on a low electronegativity atom

2. Complete octet increases stability (more of a bigger factor than formal charge)

finish the answer

answer the question

What is localized electrons?

electrons are NOT in resonance

What are delocalized electrons?

electrons are in resonance

• increases stability

How do we recognize electrons that are delocalized?

1. electrons must exist in an unhybridized p orbital that can overlap with p orbitals on neighboring atoms

2. To be delocalized, electrons must be on an sp or sp³ hybridized atom

What happens if a lone pair can participate in resonance?

The atom becomes sp² hybridized to provide a p orbital for delocalization

• so some atoms that would normally be sp³ will become sp² hybridized

Identify which of the indicated lone pairs are localized.

answer