Organic chemistry final review

Periodic trends: Electronegativity increases from…

Left to right across the table, and down to up (Towards fluorine)

Periodic trends: Atomic radii increases from

Right to left across the periodic table, and up to down (Towards Francium)

Electron affinity and ionization energy increases from

left to right across the table

Formal charge formula

(valance electron-(lone pairs (2e) + 1/2(amounts of bonds 2e each))

Rule for sigma bonds

Maximum of 1 sigma bond per bond, and minimum of 1 sigma bond per bond

Rule for pi bond

Maximum of 2 sigma bonds per bond, and minimum of 0 pi bonds per bond

A chiral center needs to have what

4 unique surrounding group

Labeling priority is based off of

how big the atomic number

Priority of hydrogen

is always 1

what if the last priority is on a wedge?

swap the location of the dash group with the wedge group, then swap the location of the two other groups with each other. reorder priority

counterclockwise

S

clockwise

R

What is the "Golden Rule" of resonance stability

The octet rule, A structure where all atoms have a full valence shell is always more stable than one with an incomplete octet.

If two resonance structures both satisfy the octet rule, how do you determine which is the "major contributor"?

Look at electronegativity. The major contributor will place a negative charge on the more electronegative atom and a positive charge on the less electronegative atom. (negative charge on oxygen is often better)

The percentage a resonance structure makes of a molecule depends on what

its stability, how well it can stabilize charges

How does charge separation affect the stability of a resonance contributor?

More charge separation generally decreases stability. A neutral structure or one with fewer formal charges is typically more stable than a structure with multiple charges.

True or False: Resonance structures represent different molecules that flip back and forth.

Resonance structures are a way to describe a single molecule with delocalized electrons; the actual molecule is a "hybrid" of all contributors.

In a Newman projection, what is the dihedral angle of a staggered conformation?

60 degrees. This minimizes repulsion between the bonds.

Why is an eclipsed conformation higher in energy than a staggered one?

Due to torsional strain. The bonds on the front and back carbons are aligned, causing maximum electron-electron repulsion between the bonding pairs.

Which conformation—staggered or eclipsed—is considered more stable?

Staggered. It is the lowest energy state because it maximizes the distance between the atoms and bonding electrons.

When comparing two acids where the acidic hydrogen is attached to atoms in the same row what is the most important factor?

Electronegativity. The more electronegative the atom, the better it stabilizes the negative charge of the conjugate base, leading to a stronger acid.

When comparing atom of the same column, why is H-I a stronger acid and H-F

Atomic Size. Iodine is much larger than Fluorine, allowing the negative charge to be "diluted" over a larger volume, which is more stabilizing than electronegativity in this context.

How does resonance affect the pKa of a molecule?

Resonance lowers pKa making the molecule more acidic

What happens to the inductive effect as an electronegative atom is moved further away from the acidic proton?

The effect decreases rapidly. Induction is distance-dependent and typically becomes negligible after three or four bond lengths.

How does the bulkiness of molecule affecting its pka

More steric hinderance, the higher the pka, so less acidic

How does the percentage of s-orbitals affecting pka

more s character means the electrons are held closer to the nucleus, which better stabilizes the negative charge of the conjugate base.

What is the relationship between the strength of an acid and the strength of its conjugate base?

They have an inverse relationship. A strong acid always produces a weak, stable conjugate base. A weak acid produces a strong, unstable conjugate base.

What is the relationship between the strength of a base and the pka of its conjugate acid?

Directly proportional. As the pKa of the conjugate acid increases, the strength of the base increases.

in acid and base reaction, the reaction favors what side?

Which ever side’s acid (acid vs conjugate acid) has a weaker (larger) pKa

What is a nucleophile

"Nucleus-loving." Electron-rich species (has a lone pair or pi-bond) that attacks an electron-deficient center. Look for negative charges or lone pairs.

Weak nucleophiles can be good…

leaving groups

What is an electrophile

"Electron-loving." Electron-deficient species that accepts an electron pair. Look for positive charges, partial positives or incomplete octet

What makes a strong vs. weak Nucleophile?

Usually carries a negative charge. Stronger nucleophiles relate to basicity. The more basic, the more nucleous loving. Weaker nucleophiles are typically stronger acids with higher pKa

What makes a good Leaving Group (LG)?

Best leaving groups are weak bases, so stronger acids, weaker nucleophiles

how to make OH a good leaving group

We can protonate OH with a strong acid to make it into H2O, which is a better leaving group

Describe SN1 reaction mechanism

Multistep reaction.

-LG leaves to form a carbocation (Where the carbocation center is positively charged

-Nucleophile breaks off and attacks. can attack from both the bottom and top of the carbocation (swaps the sterochemistry)

-Result: racemization, a combination of R and S(both bottom and top attacks). Sterochemistry is not kept in the final product.

Describe SN2

single-step reaction

-The nucleophile attacks the back side as the LG leaves

-Result: inversion of configuration. Sterochemistry is reversed and kept

SN2 preference

-Primary or secondary carbons (How many its connected to)

-Aprotic solvents (polar solvent with no O-H or N-H)

-Heavy NO on steric hinderance

-Requires a strong nucleophile and a good leaving group

-Cannot hydrogen bond

Carbocation is more stable when

It’s connected to other carbon centers. If it’s connected to three or more carbons (tertiary) most stable compared to secondary or primary. Stabilized by hycnojugation (neighboring C-H bonds sharing electron density) and induction.

SN1 preference

-Tertiary carbocation

-Doesn’t mind steric hindrance

-Protic solvent (Polar O-H or N-H)

-weak nucleophile

-Good leaving group

-can hydrogen bond

Transition state Vs intermediate state

transition state is the top of the hill where bonds are in the process of partially breaking/forming.

Intermediate state is always between two transition states, the dip in the hill.

Exothermic reaction

Releases heat (-H), products are always lower than reactants. Surrounding feels warm

(More bonds formed than bonds broken in the reaction as a whole)

Endothermic reaction

Absorbs heat from surrounding as the energy is needs to break bonds(+H). Reactant is always lower than products. The surrounding will feel cold instead. (More bonds are broken than formed)

What is Bond dissociation energy (BDE)?

Energy required to break bonds homolytically (each atom gets on electron) Breaking a bond requires input of energy, and the formation of a bond releases energy

What are the steps of a radical chain reaction

1) Initiation: Creation of radicals as they are broken homolytically. Usually by heat or UV light (radical on product side)

2) propagation: radical reacts with a stable molecule to create a new molecule (one radical on product, one on reactant). This process repeats until termination

3) termination: two radicals collide to form a stable bond, ending the chain (two radical on reactant, none on product)

How do you turn a neutral alcohol into a strong nucleophile?

Use a strong base to remove the H+ and form a negatively charged RO-

How do you change a neutral alcohol into a good leaving group

protanate it with a strong acid where the acid donates its H+ making a H2O+ that can now easily leave, making space for the carbocation.

Carbonyl is considered to be a what

good electrophile since of the partial charge induced by oxygen. The carbon is easy to attack at both the bottom and top. Saloon door metho or the x method

If a reaction coordinate diagram has three peaks and two valleys, how many steps and intermediates are there?

Three steps (three transition states) and two intermediates.

State the like dissolve

reactants will dissolve in a solvent that shares similar properties such as both being polar, protic, aprotic, nonpolar, etc

Saturated hydrocarbons with only single bonds, unreactive (C-C)

alkanes

Unsaturated hydrocarbons containing at least one double bond (C=C)

Alkene

Unsaturated hydrocarbons containing at least one triple bond

Alkynes

Saturated carbon

Saturated carbon is attached to as many hydrogens as possible

unsaturated carbon

not attached to the max amount of hydrogen due to prescence of a ring or double/triple bonds

How does branching affect speed of SN2

Branching increases steric hindrance, which blocks the nucleophile from performing the necessary backside attack, so speed is lowered

How does branching affect the rate of SN1

increases the rate as the branching stabilizes the carbocation intermediate

Positively charged with more hydronium implies

stronger acid

Carbocation stability is determined by what two factors

Stability is increased by electron-donating groups and resonance.

What makes a radical the "most stable"?

Like carbocations, radicals are electron-deficient and are stabilized by resonance and substitution.

How is "Smallest Bond Dissociation Energy" related to radical stability?

most stable radical will have the lowest (smallest) BDE. opposite is also true

Sn2 reactions have how many transition state?

one

Activation energy

The energy difference between reactant and transition state

Lower the activation energy

Faster the reaction rate

Most reactive carboxylic acid

Ester

Least reactive carbolic acid

Amides

Spectroscopy

Study of the interaction between light energy and matter.

Transmission

Light passes through a sample without being absorbed

Emission

A sample releases light (After absorbing the energy)

Absorption and filtration

A sample takes in a certain wavelength of light and blocks it from passing through. Light that isn't absorbed is what we visibly see.

Conjugation Length

Number of alternating double bonds in a row

Wavenumber

Directly proportional to energy and frequency. Higher wavenumber implies higher frequency. Represents the x-axis of the FTIR chart.

Transmittance(%)

Measures the amount of light that passes through a sample. A peak down means a light of that wavelength was absorbed.

All spectroscopy involves:

A light source, a sample, and a detector that measures light after interaction.

electromagnetic spectrum

Range of energy.

High energy affects which part of the molecule

Nuclei and core electrons (Gamma and X-rays)

Mid energy affects which part of the molecule

Affects bond vibrations (infrared)

low energy affects which part of the molecule

Affects electron distribution in bonds, specifically pi-electrons (UV and visible).

Longer wavelength means

lower frequency and lower energy

Shorter wavelength means

higher frequency and higher energy

From the highest to the lowest frequency of energy

Gamma Rays, X-rays, Ultraviolet, visible light (violet -->red), infrared, Microwave, Radio

Electronic Excitation

When a molecule absorbs visible or UV light, an electron in the pi bond gets a boost of energy and jumps from the ground state (the lowest energy and most stable) to an excited state

Energy required to excite an electron depends on what?

How well the electron can be stabilized by the molecule (Aka, total single bonds/resonance)

increase in resonance structure of a molecule...

It requires less energy to excite its electrons

Increase in conjugation length...

lower energy of absorbed light is needed to excite an electron (aka, longer wavelength of absorbed light)

The difference between a molecule with more and less conjugation length

Less conjugation length requires higher BDE, more conjugation length requires lower BDE

The color we perceive is the...

Complementary to what is absorbed

Purple filter absorbs what light?

Green light

what does FTIR stand for?

Fourier Transform Infrared Spectroscopy

What does visible light do to molecules

interact with pi bonds

What does infrared light do to molecules

Makes molecules vibrate(Strecth/bends)

A bond will only absorb infrared light if...

its vibrational frequency is matched with the light's frequency

What are the types of vibration a molecule can undergo?

Symmetrical stretching, Antisymmetrical stretching, scissoring, twisting, rocking, wagging

What is FTIR used for?

To account for the abscence or presence of a functional group

Which vibration type requires more energy (higher frequency)

Stretching

Which type of stretching requires more energy

Asymmetrical stretch

FTIR of water

multiple peaks due to the different ways it vibrates

Stretching: O-H (3500 cm-1)

Bending: H-O-H (1640cm-1)