Necessary ORGO Unit 2 stuff

How many carbons are in methane, ethane, propane, and butane?

Methane = 1, ethane = 2, propane = 3, butane = 4.

What is a methyl group?

A branch containing 1 carbon: –CH₃

What is an ethyl group?

A branch containing 2 carbons: –CH₂CH₃

What do di-, tri-, and tetra- mean?

Two, three, and four of the same substituent

What is the general formula for a simple cycloalkane with one ring?

CₙH₂ₙ: n being # of carbon (so H is double the carbon)

Why do cycloalkanes have fewer hydrogens than open-chain alkanes?

Connecting the ends to form a ring removes two hydrogens

What is angle strain?

Extra strain caused when bond angles are forced away from their preferred angles. Smaller carbon rings usually have more angle strain.

Which is more stable: eclipsed or staggered?

Staggered

What is steric strain?

Repulsion when atoms or groups that are not bonded to each other get too close together.

What is the most stable arrangement in butane?

The anti-staggered arrangement, where the two large CH₃ groups are 180° apart.

What are axial positions?

Positions pointing mostly straight up or down.

What are equatorial positions?

Positions pointing outward around the sides of the ring.

Which position is usually more stable for a methyl group: axial or equatorial?

Equatorial, because it avoids crowding with other atoms and groups.

What changes during a ring flip?

Axial positions become equatorial, and equatorial positions become axial.

How do I choose the more stable chair?

Choose the chair with more substituents in equatorial positions, especially large groups such as CH₃

What does cis mean in a ring?

Both substituents are on the same side: both up or both down.

What does trans mean in a ring?

Substituents are on opposite sides: one up and one down

Does a ring flip change cis into trans?

No. A ring flip switches axial and equatorial positions but keeps each group pointing up or down.

What should I remember about the most stable conformations?

Staggered is more stable than eclipsed; anti is especially stable for butane; equatorial is usually better for large groups on cyclohexane

meth

1

eth

2

prop

3

but

4