Chemistry Exam 2

Anti

CH3 groups have dihedral angle of 180, they’re opposite each other (more stable, lower energy)

Gauche

CH3 groups have 60 degree dihedral angle, they’re next to each other

Torsional Strain

Increase in energy caused by an eclipsed conformation

Steric Strain

Increase in energy from the same groups being too close to each other (gauche!)

Angle Strain

Increase in energy from tetrahedral angles deviating from 109.5

Larger substituents are more stable in the….

equatorial position

When you ring flip…

Stays pointing up or down, but ALL equatorial and axial flip to the other

More symmetry means what for melting point and why?

It means higher melting point because the molecules can pack together more tightly as a solid and thus require more energy/heat to melt

To draw energy vs dihedral angle diagram…

Draw energy diagram with x axis saying “180 degrees, 120, 60, 0, 60, 120, 180) and draw waves going from stable to not to stable to not based on eclipsed, staggered, anti, and gauche newman projections

Energy barrier amounts for: CH3/CH3 eclipsed:

11kJ/mol

CH3/H Eclipsed:

6kJ/mol

H/H Eclipsed:

4kJ/mol

CH3/CH3 Gauche:

3.8kJ/mol

Torsional strain

Energy increase caused by electron electron repulsion from bonds.

If the bond between two atoms is longer, it lessens the torsional strain for the overall molecule

A wedge represents

Up

A dash respresents

Down

Oxidation

A C-Z bond is formed or a H bond is broken

Reduction

A C-Z bond is broken and an H bond is formed (they can cancel out)

Complete combustion gives you

CO2 and H2O

Incomplete Combustion gives you

CO and H2O (Amount of the two products is the same as in the complete reaction!)

What goes over the arrow of a reaction?

Reagents, catalysts, heat (Δ) or light (hv), or a solVENT

For combustion reaction arrows…

Write “flame” above the arrow, the O2 below the arrow, and put heat in the products

When balancing a combustion reaction and need a half value…

Multiply every number by 2! So then it can be whole

Lipids are unlike any other class of biomolecules, because they are defined by

A physical property, not a functional group

Lipids are

Soluble in organic solvents but insoluble in water

Oils are

hydrocarbons!

“fat-soluble” means

largely non-polar, like alkanes so will dissolve

Look out for ANGLE STRAIN!

If something tetrahedral becomes 90 degrees or anything other than 109.5 the angle strain makes that something VERY reactive

Enantiomers

Non-superimposable mirror images

Diastereomers

Stereoisomers that are not mirror images

Chiral compounds

Non-superimposable mirror images (enantiomers) with no plane of symmetry and a tetrahedral stereogenic center

Achiral

Superimposable mirror images, plane of symmetry, no tetrahedral stereogenic center

Meso Compound

Has two stereogenic centers, a plane of symmetry, and is achiral

An optically active solution contains

a chiral compound

An optically inactive solution contains one of these:

achiral compound, meso compound, or a racemic mixture of two enantiomers

Enantiomer Properties

Their physical properties (boiling point, melting point, density, solubility) are the same, but their optical properties are different

d (+)

dextrorotatory, rotates light to the right/clockwise

l (-)

levorotatory, rotates light to the left/counterclockwise

Polarizing light works by

Filtering the direction of the light to only go one way, before passing through a solution that may or may rotate that light (if it’s optically active)

Enantiomeric Excess =

specific rotation/observed rotation *100

Stereocenters in enantiomers

Are all opposite

Stereocenters in diastereomers

one is in common, the other is opposite

Formula for enantiomeric excess

ee = percent of major enantiomer minus percent of minor enantiomer

For a mixture, the observed specific rotation is

the weighted average ex/ (0.3)(2.5) + (0.7)(-2.5) = -10

Priority is based on…

ATOMIC NUMBER!!! NOT electronegativity

Reaction Rate is affected by

Heat (higher kinetic energy), concentration (more collisions) and energy of activation (higher means slower)

RR is NOT affected by

Gibbs free energy, Keq, or enthalpy

If Keq is greater than one…

Delta G is negative

If Keq is less than 1

Delta G is positive

Rate constant is represented by

K

A high Ea corresponds to

A low K

In a concerted mechanism, the rate equation contains

ALL reactants involved

In a stepwise mechanism,

it contains ONLY reactants involved up to and including the rate-determining step

order of a rate equation equals

the sum of the exponents of the concentration terms in the rate equation.

How do catalysts accelerate a reaction?

By lowering the Ea

When a catalyst quickens a reaction, what’s not affected is the

the sum of the exponents of the concentration terms in the rate equation.

Key for Newman Projections to Line Notation

left side = into page

right side = towards you

middle = in plane of page

bottom half = pointing down

top half = pointing up

Conformers

Same connectivity and everything, you just need to rotate something to make it the same molecule