Chem 240: Ch#03- An Intro To Organic Reactions And Their Mechanisms

Front 1

Substitution:

Back 1

- The characteristic reactions of saturated compounds & of aromatic compounds

- one group replaces another

Front 2

Addition:

Back 2

- Characteristic of compounds w/ multiple bonds

(all parts of the adding reagent appear in the product, 2 molecules become one)

Front 3

Elimination:

Back 3

- The opposite of addition

- One molecule loses the elements of another small molecule

- gives us a method for preparing compounds w/ double and triple bonds

Front 4

Rearrangement:

Back 4

- molecules undergoes a reorganization of its constituent parts

Front 5

Reactions of organic chemistry always involve the making and breaking of what kind of bonds?

Back 5

covalent bonds

Front 6

Heterolysis:

Back 6

(greek: hetero means different, + lysis means lossening/cleaveage)

- the breaking of bond that leaves one fragment w/ both e-s & the other fragment with an empty orbital

- produces charged fragments (ions)

Front 7

Homolytic:

Back 7

(greek: homo means same, +lysis means loosening/ cleaveage)

- the bond breaks so that each fragment takes away one of the e-s of the bond.

- normally requires that the bond be polarized.

Front 8

Bronsted-Lowry acid:

Back 8

a substance that can donate (lose) a proton

Front 9

Bronsted-Lowry base:

Back 9

a substance that can accept (remove) a proton.

Front 10

Conjugate base:

Back 10

molecule/ ion that forms when an acid loses its proton

Front 11

Conjugate acid:

Back 11

molecule or ion that forms when a base accepts a proton.

Front 12

Some other strong acids that completely transfer a proton when dissolved in water:

Back 12

Front 13

Lewis acid:

Back 13

e- pair acceptor

Front 14

Lewis base:

Back 14

e- pair donor

Front 15

What is one key concept that is fundamental to reactivity?

Back 15

the attraction of oppositely charged species

Front 16

Heterolysis of a bond to a carbon atom can lead to either which two ions?

Back 16

1. a carbocation

2. a carbanion

Front 17

Carbocation:

Back 17

- positively charge on the carbon atom

- e- deficient therefore are Lewis acids

- most are short-lived & highly reactive

- react rapidly w/ Lewis bases molecules or ions that can donate the e- pair that they need to achieve a stable octect of e-s.

Front 18

Carbanions:

Back 18

- negatively charged carbon atom

- are Lewis bases

- seek protons or (+) centered molecules to which they can donate e-s to neutralized their (-) charge

Front 19

Electrophiles:

Back 19

reagents which in their reactions seek the extra e-s that will give them a stable valance shell of electrons

- all Lewis acids including protons

(ex: carbocation)

Front 20

Nucleophile:

Back 20

reagents that seek a proton or some other (+) center

(ex: carboanion)

Front 21

What does a curve arrow represent in a reaction mechanism?

Back 21

the curved arrow represents the movement of electrons

- the curved arrow begins with a covalent bond or unshared e- pair (a site of higher e- density) and points toward a site of e- deficiency

Front 22

Equilibrium constant:

Back 22

Front 23

acidity constant:

Back 23

when water is essentially constant ~ diluted aq. soln.

- a larger value of acidity constant means the acid is a strong acid and a small value means the acid is a weak acid.

- acidity constant of ~ 10 will completely dissociate in water

Front 24

Back 24

Front 25

What does the value of pKa represent?

Back 25

The larger the value of the pKa the weaker the acid

Front 26

Table 3.1: Relative strength of selected acids and their conjugate bases:

Back 26

Front 27

sp3 (single bonds) pKa?

Back 27

~ 50+

Front 28

sp2 (double bonds) pKa?

Back 28

~45

Front 29

sp (triple bonds)pKa?

Back 29

~25

Front 30

low pKa means?

Back 30

stronger acid

Front 31

the more electron dense the higher or lower the pKa?

Back 31

lower the pKa

Front 32

pKa for pure water?

Back 32

15.7

Front 33

Strength of bases:

Back 33

The stronger the acid, the weaker will be its conjugate base.
therefore,
The larger the pKa of the conjugate acid, the stronger the base.

Front 34

amines are weak or strong bases or acids?

Back 34

typically they are weak bases

Front 35

The more stable an acids conjugate base is, the weaker or stronger the acid?

Back 35

stronger

Front 36

reactions favor side with higher or lower pKa?

Back 36

lower

Front 37

The strength of a Bronsted-Lowry acid depends on what?

Back 37

on the extent to which a proton can be separated from it and transferred to a base.

Front 38

Bond strength to the proton decreases as we move down the column why?

Back 38

mainly due to decreasing effectiveness of orbital overlap between hydrogen 1s and the orbitals of successively larger elements in the column.

Front 39

Looking at the rows in the periodic table how does acidity increase?

Back 39

from left to right.

- bond strengths vary somewhat, but the predominate factor becomes the electronegativity of the atom bonded to the hydrogen.

Front 40

Trend in acidity within the periodic table:

Back 40

Front 41

what are the pKa of ethyne, ethene, and ethane? Why such pKa?

Back 41

because of the hybridization state of carbon in each compound.

- having more s character means that the e-s of the anion will, on the avg. be lower in energy, and the anion will be more stable.

Front 42

Energy:

Back 42

The capacity to do work

Front 43

Kinetic energy:

Back 43

- the energy an object has because of its motion

KE= (1/2)m(v^2)

Front 44

potential energy:

Back 44

- stored energy

- exist only when an attractive/repulsive force exist between objects

Front 45

Chemical energy is a form of what kind of energy?

Back 45

potential energy

b/c it exists because attractive and repulsive electrical forces exist between different pieces of the molecules.

Front 46

The relative stability of a system is inversely related to its relative potential energy. This means what?

Back 46

the more potential energy an object has, the less stable it is.

Front 47

Looking at covalent bonds the state of greatest potential energy is what state of the atom?

Back 47

the state of free atoms.
(atoms are not bonded to each other @ all)

Front 48

Heat of reaction:

Back 48

Measures the change in enthalpy of the atoms of the reactants as they are converted to products.

Front 49

Are carboxylic acids weak or strong acids? range of pKa?

Back 49

weak acids

pKa:3-5

Front 50

pKa of alcohols?

Back 50

pKa: 15-18

(essentially do not give up a proton unless exposed to a very strong base)

Front 51

dispersal of charge always makes a species ______?

Back 51

more stable

Front 52

What creates a stronger acid?

Back 52

1. a more stable conjugate base

-------- the delocalizaiton effect by resonance.

-------- an inductive electron-withdrawing effect (stabilizing charge throughout the atom)

-------- the larger the molecule the lesser e- withdraw effect.

Front 53

Protic solvent:

Back 53

one that has a H atom attached to a strongly electronegative element such as oxygen or nitrogen

ex: water

Front 54

What occurs during solvation:

Back 54

the solvation of any species decreases the entropy of the solvent b/c the solvent molecules become much more ordered as they surround molecules of the solute.

Front 55

If an organic compound contains an atom with an unshared e- pair, it is a potential ____?

Back 55

base

Front 56

What compounds act as a base when treated with solutions of strong acids such as HCl, HBr, HI, H2SO4...

Back 56

alcohols, ethers, carbonyl groups. The unshared electrons of the compounds remove the proton from the strong acid.

Front 57

How do alkenes act like bases?

Back 57

react w/ a strong acid by accepting a proton.
- e- pair of pi bond of alkene is used to form a bond between one carbon of the alkene & the proton donated by the strong acid.
-- 2 bonds break:
1. pi bond of the double bond
2. bond of proton and acid
-- 1 bond forms:
1. bond between carbon of the alkene & the proton.

Front 58

Leveling effect (of the solvent):

Back 58

the solvent donates a proton to any strong base stronger than a hydroide ion (if solvent is water) therefore,
--- not possible to use a base stronger than hydroxide ion in aq. soln.

Front 59

What solvents can then be used for strong bases stronger than hydroxide ion?

Back 59

solvents that are weaker acids than water such as hexane, diethyl ether... they will not dontate a proton.

Front 60

Charges are more stable on some atoms than others, what are some rules to follow when looking at the negative charge on a deprotenated ion?

Back 60

1. Negative charges are more stable on more electronegative atom. (electronegativity increases as you go up and to the right on the periodic table)

2. Negative charges are more stable on larger atoms (size of atoms increases as you go down the periodic table. negative charges perfer to rest on larger atoms b/c larger atoms allow the negative charge to delocalize over a larger space)

3. a negative charge is more stable on a larger atom than on an electronegative atom

4. negative charges prefer to rest on sp-hybridized atoms over sp2-hybridized atoms, and they prefer sp2 over sp3 atoms.