Week 6 Textbook

Question 1

curved arrow notation

Answer 1

depicts the flow of electrons during a reaction
-notation focuses on the valence electrons and how their overall movements result in the formation and breaking of bonds

Question 2

pi bonds

Answer 2

The π bonds in double or triple bonds are weaker and more reactive than σ bonds. In line-structure diagrams, π bonds always appear as parallel bond lines, and they react in predictable ways

Question 3

heteroatoms

Answer 3

heteroatoms (any atom besides C or H) often possess one or more non-bonded pairs of electrons (lone pairs) that can participate in reactions

since the electronegativities of such atoms differ from that of carbon, the electron density around a heteroatom is NOT the same as around the carbon atom it is bonded to, a feature that tends to induce reactions

a π bond directly connected to a heteroatom should be considered as part of a single functional group involving the bond and the heteroatom

Question 4

formal charges

Answer 4

The presence of a formal charge on a molecule RAISES its energy state relative to its uncharged form, often facilitating a chemical rxn

Negative charges on atoms are typically associated with non-bonded electron pairs, which can be shared with other atoms to form bonds

Positive formal charges indicate sites that may accept electrons from another atom
–if a positive charge exists on an atom that has an incomplete octet, the atom can accept electrons to form bonds
–if the positively charged atom has a complete octet, it ONLY accepts a pair of electrons if one of its other bonds BREAKS

Question 5

amide

Answer 5

when heteroatoms are connected to or near pi bonds, they interact to form a single functional group called an amide

Question 6

When bonds are broken in organic reactions…

Answer 6

the electrons generally flow to the more electronegative atom or the best electron attractor

Question 7

When bonds involving positive charges break…

Answer 7

the electrons move toward the positive charge (a positively charged atom is a very strong electron attractor)

Question 8

formal charge calculation

Answer 8

(# electrons in atom’s neutral valence) - (# bonds) - (# non-bonding electrons)

Question 9

formal charge

Answer 9

The formal charge can be treated as a simple integer that decreases or increases by one unit depending on the direction a mechanistic arrow points

When a double-barb arrow points to an atom, electrons are moving toward the atom, and that atom’s integer decreases by one unit

Thus, an atom with a formal charge of +1 would become neutral, and a neutral atom would acquire a formal charge of −1. Similarly, when a double-barb arrow points away from an atom, electrons are moving away from the atom and that atom’s integer increases by one

Thus, an atom with a formal charge of −1 would become neutral, and a neutral atom would acquire a formal charge of +1.

Question 10

intermolecular rxn

Answer 10

When separate molecules react, the process is called an intermolecular reaction

The functional groups on one molecule interact with the functional groups on another molecule, resulting in the formation of products

Question 11

intramolecular rxn

Answer 11

Reactions that occur within a molecule are called intramolecular reactions

These reactions can occur when a molecule contains two or more functional groups that are arranged so they can interact

The flows of electrons are the same as those in intermolecular reactions

Intramolecular reactions can be very fast because the functional groups are positioned CLOSE to each other
–intramolecular rxns are especially favorable when they form five- or six-membered rings

Question 12

how do electrons flow in rxn mechanisms

Answer 12

Bonds form when one atom shares electrons with another atom

In reaction mechanisms, electrons flow from an area of high electron density (lone pair or bond) to an area of low electron density (atom lacking octet or positively charged atom)

Question 13

true or false: the positive charge on an sp2 atom will lead to resonance

Answer 13

true

Question 14

what does the bronsted theory say about acids and bases

Answer 14

acids are proton (H+) donors

bases are proton acceptors

The behavior of a typical Brønsted acid can be represented as an equilibrium dissociation of the acid (HA) into a proton (H+) and conjugate base (A−)

Question 15

how to tell which molecule is the acid

Answer 15

An acid must have a hydrogen atom with a partial positive charge on it

Look for hydrogens attached to more electronegative atoms, especially ones with a positive charge or with nearby electron-withdrawing groups

In this reaction, there is a hydrogen atom bonded to an electronegative oxygen atom

The electronegativity difference between these atoms creates a polarized bond with a partial positive charge on the hydrogen atom
–therefore, this molecule is the acid

Question 16

curved arrows on acid + base

Answer 16

Since a base is always electron rich and an acid is always electron poor, the curved arrows in an acid–base reaction always begin at the base and end at the acid

Question 17

strength of an acid

Answer 17

The strength of an acid relative to another acid is a reflection of the extent of the dissociation of each into their corresponding conjugate bases

Strong acids dissociate much more readily than weak acids

The dissociation of an acid is described by its logarithmic dissociation constant, pKa, which indicates the strength of that acid

Question 18

pKa

Answer 18

indicates the strength of that acid

This constant is a measure of the difference between the free energy (G) of the acid and that of its dissociation products

Very strong acids have a negative ΔG°, and their dissociation is exothermic

Question 19

strong vs weak acids

Answer 19

strong = neg. delta G

weak= positive delta G

Question 20

what does the strength of 2 acids (or 2 bases) in an orgo rxn tell you

Answer 20

determines the order of the mechanistic steps during that reaction

Question 21

strength of a base

Answer 21

The strength of a base is related to its ability to accommodate (i.e., stabilize) a negative charge

When a charge is stabilized, the energy of the charged species is reduced

Bases that stabilize negative charges readily are WEAK (with a less positive ΔG°), while bases that do not stabilize negative charges as much are STRONG (with a more positive ΔG°).

Question 22

5 factors that contribute to charge stabilization

Answer 22

electronegativity, atomic size, induction, hybridization, and delocalization (resonance)

Question 23

electronegativity and bases

Answer 23

the electronegativity of the atom carrying the negative charge has a large impact on conjugate base stability

Electronegativity increases from left to right across the periodic table, so bases in which the atom carrying the negative charge lies farthest to the right stabilize negative charges the most

Question 24

conj bases of an alcohol and amine

Answer 24

alkoxide and amide

Oxygen lies to the right of nitrogen on the periodic table and is, therefore, MORE electronegative
–so, oxygen has a higher affinity for electrons, and a negative charge on oxygen is more stabilized than one on nitrogen

Consequently, the alkoxide is a weaker base than the amide

Because the alkoxide is the weaker base, the corresponding parent acid, the alcohol, is the stronger acid

Question 25

induction

Answer 25

the removal of electron density from an atom by a strongly electronegative atom nearby The presence of electron-attracting groups (usually called electron-withdrawing groups) near a negative charge can spread out the electrons associated with the charged atom by induction The electronegativity of atoms near the negative charge causes the electrons to be pulled toward the electronegative atom(s) --this increases the volume over which these electrons are distributed (delocalizes them) and stabilizes the negatively charged base

Question 26

induction and delocalization involve which bonds

Answer 26

Induction occurs through σ bonds, while delocalization (described by resonance) involves π bonds.

Question 27

inducive effects

Answer 27

Inductive effects occur through bonds The strength of inductive effects depends on the electronegativity of the atoms involved, not the size of those atoms The strength of induction depends on how many inductively withdrawing atoms are present and how close these atoms are to the negative charge.

Question 28

hybridization

Answer 28

Since s orbitals are lower in energy than p orbitals, hybrid orbitals with more s character are lower in energy Unpaired electrons are more stable in sp orbitals than in sp3 orbitals A lower energy orbital makes a negatively charged conjugate base more stable and, therefore, weaker

Question 29

acid base rxns

Answer 29

Acid–base reactions in organic chemistry sometimes involve positively charged acids that produce neutral conjugate bases For example, a protonated alcohol oxonium can act as a proton donor (acid), forming a neutrally charged alcohol as the conjugate base

Question 30

electronegativity

Answer 30

Electronegative atoms destabilize positive charges, so charged acids in which the element carrying the positive charge appears to the right side of the periodic table are less stable than acids in which the charged atom lies to the left of the periodic table Acids with positive charge on more electronegative atoms are more acidic, and their conjugate bases are correspondingly less basic.

Question 31

atomic size and protonation

Answer 31

Large atoms are not as easily protonated as smaller atoms are More difficult protonation implies less stability for the positively charged partners involving large atoms.

Question 32

induction

Answer 32

Nearby electronegative atoms increase the effective positive charge on an atom They do this by withdrawing extra electron density from the positively charged atom, making the atom even more positive This effect makes a positively charged molecule less stable and, therefore, a stronger acid.

Question 33

pKa

Answer 33

Acid strength has been measured accurately for many substances and is commonly expressed in terms of the logarithmic acid dissociation constant pKa. A lower pKa indicates a stronger acid; a higher pKa shows a weaker acid The strongest bases are those for which the conjugate acids have the highest pKa values

Question 34

Quantitative prediction of equilibria

Answer 34

the behaviour of organic acids and bases when mixed determines the order in which bonds are broken and formed The key to predicting the results of acid–base reactions is determining the equilibrium point, which indicates if the equilibrium will favor the reactants or the products Equilibrium reactions tend to shift toward the more STABLE materials Therefore, acid–base equilibria favor weaker acids and bases; that is, at equilibrium, the concentration of the weaker acid and base is greater than that of the stronger ones

Question 35

protonation states at various pH values

Answer 35

The pKa of an acid can be used to predict the protonation state at various pH values. Acids are primarily in their protonated form when the pH is less than the pKa, and they deprotonate when the pH is greater than the pKa.

Question 36

protonated and deprotonated form

Answer 36

The terms protonated form and deprotonated form refer to their position on an acid dissociation equation (reactants or products), not to whether a molecule is charged or not.

Question 37

lewis acid theory

Answer 37

classifies acids as electron pair acceptors and bases as electron pair donors. Lewis acids function just like protons (H+) do. Metals are commonly used as Lewis acids, and these react with the strongest bases present

Question 38

electronegativity and stability

Answer 38

If the charges are carried on heteroatoms in the same row of the periodic table, use electronegativity to determine relative stability More electronegative elements stabilize negative charges, while positive charges will be less stable if found on these atoms

Question 39

charge and stability

Answer 39

If the charges are carried on heteroatoms in the same column of the periodic table, use size to determine relative stability. Large atoms stabilize both positive and negative charges by distributing them over a larger volume. Therefore, atoms lower in the periodic table will give more stable charged species than atoms in rows above.

Question 40

induction and stability

Answer 40

The presence of electronegative atoms close to a charge can influence the stability of that charge through induction Electronegative atoms withdraw electrons. This effect tends to stabilize a nearby negative charge by distributing it over a larger volume. Similarly, nearby electronegative atoms will destabilize positive charges The magnitude of the induction effects depends on the number of electronegative atoms present, the electronegativity of these atoms, and their proximity to the charged site.

Question 41

how do electrons flow in rxn mechanisms?

Answer 41

from an area of high electron density (lone pair or bond) to an area of low electron density (atom lacking octet or positively charged atom)

Question 42

when a bond involving a positive charge breaks, its electrons flow twd...

Answer 42

positive charge

Question 43

if the double barb arrow points AWAY from atom...

Answer 43

the formal charge integer on atom increases by one unit

Question 44

if arrow points twd atom

Answer 44

formal charge decreases by 1

Question 45

how do curved arrows point in an acid-base rxn?

Answer 45

Since a base is always electron rich and an acid is always electron poor, the curved arrows in an acid–base reaction always begin at the base and end at the acid.