exam 2 (chapters 3 & 4)

Question 1

bronsted-lowry vs lewis definitions of acids and bases

Answer 1

bronsted-lowry:
acid = proton donor (H+)
base = proton acceptor (H+)

lewis theory:
acid = electron pair acceptor (electrophile)
base = electron pair donors (nucleophile)

Question 2

pKa value and acid strength

Answer 2

lower pKa = stronger acid (more likely to donate a proton)

Question 3

strength of acid & conjugate base and vice versa

Answer 3

• stronger the acid = weaker the conjugate base
• weaker the acid = stronger the conjugate base

Question 4

predicting acid-base reactions

Answer 4

acid base reactions only happen if the proton transfer goes from stronger acid to weaker acid (or stronger base to weaker base)

• otherwise reaction does not happen
• so equilibrium favors formation of the one with the more stable neg. charge (more stable conjugate base)

Question 5

carboxylic acids, alcohols, and amines acidity

Answer 5

carboxylic acids (-COOH): acidic

alcohols (-OH): weak acids

amines (-NH2): basic

Question 6

how to identify bronsted-lowery acids/bases + how to identify lewis acids/bases

Answer 6

bronsted Lowry acid: proton donor (H+), look for molecules with protons (H atoms) that can be donated
- tip: if molecule has easily detachable hydrogen (esp if bonded to an electronegative atom like O, N, or halogen) then most likely a bronsted-lowry acid

bronsted-lowry base: proton (H+) acceptor, look for molecules with lone pairs that can grab a proton
- common examples: ammonia (NH3), amines (-NH2)

lewis acids: electron pair acceptor, look for molecules with electron deficient that can accept a pair of electrons
- often includes cations (positively charged), electron deficient molecules (BF3, AlCl3)

lewis bases: electron pair donor, look for molecules with lone pairs that can donate an electron pair

Question 7

leveling effect of water

Answer 7

phenomenon where water as a solvent “levels” strength of all strong acids or strong bases, making them appear equally strong no matter how strong it originally was

acids: any acid stronger than H3O+ dissolved in water = acid transfers proton to water to produce H3O+ = strongest acid that can exist is H3O+

bases: any base stronger than OH- dissolved in water = base takes proton from water = strongest base that exists now is OH-

• happens because water can either be a base or an acid and either donate proton or accept

Question 8

how to cancel out leveling effect

Answer 8

use a different solvent

for strong acids: use solvents less basic than water = strong acids remain strong acids (b/c solvent cannot fully convert them into H3O+)

for strong bases: use solvents less acidic so they remain stronger than OH-

Question 9

4 factors for charge stabilization (conj. base): 1. atom

Answer 9

ARIO - ATOM

more stable the charge = stronger acid b/c weaker conj. base

more electronegative the atom the neg. charge is on = more stable the charge (towards flourine) if in the same row

if in the same column (up and down) then bigger the atom = more stable the charge b/c charge is spread out over large volume vs. stuck in one spot

Question 10

how to draw the conjugate base for an acid

Answer 10

remove the H and replace it with a lone pair and add the negative charge

Question 11

4 factors for charge stabilization (conj. base): 2. resonance

Answer 11

ARIO - RESONANCE

if same atom, then go down to resonance

delocalized charge is more stable than localized charge

delocalized = spread out over atom (resonance)
localized = stuck in one place (no resonance)
- more atoms sharing charge = better

however, 1 oxygen is better than many carbons
- so better for charge to be on the more electronegative atom and being shared with another electronegative atom than multiple non-electronegative atoms

Question 12

4 factors for charge stabilization (conj. base): 3. induction

Answer 12

ARIO - INDUCTION

• electron withdrawing groups can make a molecule more acidic (weaker base b/c of stabilized charge) by pulling e- density towards them (so then the other molecule has to pull e- density from the neg. charge making it more stable)
• the more you pull you have on charge = the more stable it is
• induction also falls off with distance - if the electronegative atoms are closer, they have more of an effect, if they’re 2 carbons away, then not so much

Question 13

4 factors for charge stabilization (conj. base): 4. orbitals

Answer 13

ARIO - ORBITAL

• if no other factors are applicable, then look at the orbital type

higher the s character, closer the electrons are held to the nucleus = more stable neg. charge

• more s character in sp vs sp3

so, a neg. charge on a triple bond is more stable than a neg. charge on a double or single bond

Question 14

electrophiles vs. nucleophiles & how to identify them

Answer 14

electrophiles: “electron loving”, electron-deficient species that accept electrons
- have a positive charge, partial positive charge due to polar bond, an incomplete octet

carbonyl is electrophilic b/c oxygen pulls e- density away from carbon, making it slightly positive

nucleophiles: “nucleus loving”, electron rich species that can donate electrons
- usually have a negative charge, lone pairs of electrons, or pi bonds (alkenes or alkynes)

Question 15

effect of alkyl groups (carbon atoms) on charge stabilization

Answer 15

alkyls: branched molecules that contain only carbon and full saturation of H’s

• alkyl groups are e- donating so they destabilize the neg. charge

b/c the trend is the more pull = more stable charge, but here there is more push

so if there is a large alkyl group present, it destabilizes the charge

Question 16

showing an acid-base mechanism using curved arrows

Answer 16

• very straight forward in acid-base reactions because only 1 step

always 2 arrows- one from base grabbing the proton (H) and the other from bond b/w proton & atom to the atom thats connected to the proton

• different from resonance b/c allowed to break single bonds here since showing movement of electrons

Question 17

single barbed vs. double barbed arrows to show mechanism

Answer 17

single barbed: used to show movement of a single electron, mostly used in radical reactions (which involve unpaired electrons)

double barbed: represents movement of 2 electrons (electron pair), mostly used in acid base reactions

Question 18

electrophiles and nucleophiles in Lewis acid-base reactions

Answer 18

all lewis acids are electrophiles and all lewis bases are nucleophiles

Question 19

carbocation & carboanion + lewis bases/acids

Answer 19

carbocations: have the + charge on carbon, only 3 bonds = are lewis acids b/c electron deficient & also electrophiles

carboanions: have = charge on carbon, have the electron pair = are lewis bases b/c electron dense & also nucleophiles

Question 20

solubility of amines

Answer 20

low molecular weight = very soluble in water

amines with higher molecular weight = decreased water solubility.

solubility of amines in water decreases as molecular weight increases

• but water insoluble amines readily dissolve in HCl b/c the acid turns them into soluble salts

Question 21

neutral functional groups

Answer 21

aldehydes, ketones, ester

Question 22

how to tell where/which hydrogen atom will be extracted from the base

Answer 22

hydrogens that leave behind more stable conj. bases = most acidic hydrogen

for ex. COOH is a strong acid b/c COO- is stabilized by resonance when the H leaves

more acidic hydrogens are:
- attached to electronegative atoms
- inductive effect (near electronegative atoms) b/c the charge is pulled towards electronegative atom and away from H, making it easier to remove
- on triple bonds, or double bonds

Question 23

pKa table - how to figure out which way the reaction will go

Answer 23

• look up the pKa values of the acid and the conjugate acid and compare them
• acid needs to have lower pKa than the conj acid for the reaction to favor the right
• each group on list can extract protons from all the groups above it

Question 24

effect of charge on acidity

Answer 24

acidity increases with increasing positive charge on an atom

• b/c eager to lose charge to want to be neutral so more likely to want to donate the proton (has to do with + charge, not the # of H)
• neg. charge = will have tendency to accept a proton to regain neutral

Question 25

protic solvent

Answer 25

solvent that can donate a proton (H+)

Question 26

Deuterium and Tritium

Answer 26

both isotopes of hydrogen but they are heavier and have slightly different properties

Question 27

how to determine which solvent can be used to dissolve a base/acid

Answer 27

base = tendency to accept H+ acid = tendency to donate H+ so, in order to have solubility, you don't want a reaction so pick something that will either NOT make the base accept or acid donate for base, choose the solvent that has a **higher or same pKa than the solute** for acid, choose the solvent that has a **lower or same pKa than solute**

Question 28

predicting reactions

Answer 28

- identify strong bases like NaNH2 and CH3Li = they often cause **deprotonation reactions** - acid-base reactions are not substitution reactions, just proton transfer reactions (DONT OVERCOMPLICATE IT!!)

Question 29

2 fundamental types of energy

Answer 29

**kinetic energy**: energy due to motion, KE = 1/2mv^2 **potential energy**: stored energy, *chemical form is a type of potential energy* - the more potential energy an object is, the less stable it is (why charged species are not stable - b/c they have a lot of potential energy) - most stable when atoms are at ideal internuclear distance from each other (not too far not too close)

Question 30

explain ∆G = ∆H-T∆S + what it takes to have a neg. ∆G sign

Answer 30

**∆G = + ∆G = formation of products at equilibrium is unfavorable - ∆G = formation of products is favorable **∆H = entalphy is heat content** (potential energy) - sign when exothermic + sign when endothermic *when bonds are formed, energy is released and sign is neg.* **∆S = change in disorder (entropy)** - sign = disorder is decreasing, number of molecules on the reactants side is more + sign = disorder is increasing, number of molecules on the products side is more **-∆G sign = -∆H value and +∆S value**

Question 31

how to tell if acid/base reactions are exothermic or not and ∆G value

Answer 31

want ∆G to be negative - that means the proton transfer will occur in the forward direction - most acid/base reactions are exothermic, unless they just dont occur

Question 32

affect of aromatic group on acidity

Answer 32

aromatic group stabilizes the neg. charge making the compound more acidic ex. phenol is more acidic than cyclohexanol b/c it has the double bonded ring

Question 33

how does the number of constitutional isomers increase

Answer 33

the number of constitutional isomers increases rapidly with the carbon number

Question 34

common names vs IUPAC names of alcohols

Answer 34

common names: -yl alcohol IUPAC: -ol

Question 35

difference b/w iso-, sec-, tert-, neo-

Answer 35

**iso**: second to last carbon has a methyl group attached to it, chain is continuous except for that one methyl branch **sec**: functional group or methyl group is attached to a secondary carbon (carbon thats bonded to 2 other carbons) - *only useful when chain is 4 carbons exactly (not helpful for more or less)* **tert**: indicates functional group or methyl group is attached to a tertiary carbon (carbon attached to 3 other carbons) formula: (CH₃)₃C- - subclass of neo branching **neo**: quaternary (carbon attached to 4 other carbons) is bonded near the functional/methyl group formula: (CH₃)₃CCH₂- - theres an additional CH2 group - *only used when there are 5 or more carbon atoms, not possible for butyl*

Question 36

how to name branched-chain alkanes

Answer 36

- when 1 hydrogen removed, becomes alkyl group and gets named with **-yl at the end instead of -ane** (when attached as a substituent) - use the **longest parent chain** - start numbering so that the **substituent gets the lowest number** - if multiple substituents, list the numbers of *each* (even if repeated twice) and **use di, tri, tetra, etc.** (sec and tert also dont count for alphabetization, but iso and neo do) - alphabetize the substituents and **disregard "di", "tri," when alphabetizing**

Question 37

naming branched-chain alkanes: what to do when 2 chains of equal length compare for selection of parent chain

Answer 37

choose the chain with the greater number of substituents (so that it includes as many substituent groups as possible)

Question 38

naming branched-chain alkanes: what to do when both sides give you the same first number for the substituent

Answer 38

choose the numbering order that gives the lower number at the first point of difference *so if the next substituent is 3 from one direction and 4 from the other, use the one that gives it 3*

Question 39

how to classify hydrogen atoms

Answer 39

**hydrogen atoms are classified based on the carbon atom to which they are attached** - ex. hydrogen atom attached to a primary carbon atom is a primary hydrogen atom and so forth

Question 40

what parent chain to pick when there is a functional group

Answer 40

make sure the parent chain contains the functional group (even if its not necessarily the longest)

Question 41

how to name when there are 2 hydroxyl groups (alcohols)

Answer 41

**-diol** - goes all the way at the end (after parent chain) **common system**: glycols ex. 1,2-ethanediol common name of that: ethylene glycol

Question 42

naming cycloalkanes (numbering them really)

Answer 42

- very similar to naming branches alkanes, main difference is in the rules and procedures in the numbering system **start numbering at a substituted ring atom** (b/c cycle just go in a circle on and on) - for **multiple substituents**: number so that the substituents get the lowest possible numbers, also at point of difference

Question 43

carbon atoms + bonds

Answer 43

- carbon forms very **strong bonds with itself** and can therefore form stable chains - carbon-carbon **single bonds can rotate freely** and the 3D shapes (conformations) can vary significantly in energy - forming a ring decreases the hydrogen number by 2 - cycloalkanes of less than 8 carbons **cannot be turned inside out** without breaking carbon-carbon bonds = gives rise to cis and trans isomers that cannot be interconverted

Question 44

neopentane IUPAC name

Answer 44

2-2, dimethylpropane

Question 45

naming parent chains with cycloalkanes

Answer 45

- rings are senior to chains if composed of the same elements so **cycloalkane becomes the parent chain** - but in situations of 2 rings, the ring with more atoms get the parent chain name (**bigger ring = parent chain**) - when both rings are the same size, **chain becomes the parent chain** instead of the rings (ex. 1,2-dicylco hexyl ethane)

Question 46

naming bicyclic cycloalkanes

Answer 46

- start from the bridgehead that gives the substituent (if any) the lowest number - start from bridgehead and go through the biggest ring first [ ] = number of carbons on both sides and between the bridgehead, bigger number first ex. 1-isopropyl bicycle[2,2,2] octane

Question 47

naming alkenes: double bonds

Answer 47

- make sure parent chain includes the double bond - begin numbering at the end of the chain nearer to the double bond *- ane* name becomes *-ene* and put the number of the double bond (where the double bond starts) before parent chain name

Question 48

numbering double bond in cycloalkenes

Answer 48

start numbering where the **double bond starts and go towards where it ends** and also make sure the substituent groups get the lower number at the point of difference - but if functional group then **functional group gets priority over the double bond** and gets the lower number

Question 49

difference between vinyl and allyl

Answer 49

**vinyl**: 2-carbon chain with a double bond, directly connected to the parent structure **allyl**: 3-carbon chain with a double bond, with the double bond one carbon away from the parent structure (*remember it because it looks like an A*) ex. vinylcyclopropane

Question 50

numbering branched chains: functional group, double bond, triple bond

Answer 50

hierarchy: - functional group - double bond - triple bond no FG = double bond gets lower # no FG and no double bond = triple bond gets lower # no FG, double, or triple bond = substituent gets lower # **double bond gets preference over the triple bond if there are both - it gets the lower number**

Question 51

which prefixes count for alphabetization and which dont?

Answer 51

iso and neo count - tert and sec dont

Question 52

physical properties of alkanes + cycloalkanes at 25ºC and 1 atm pressure

Answer 52

- first 4 members of the homologous series of unbranched alkanes are **gases** - C5-C17 unbranched alkanes (pentane to heptadecane) are **liquids** - unbranched alkanes with 18 and more carbon atoms are **solids** boiling point increases as number of carbon atoms increases (for unbranched) *same with cycloalkanes - but they have higher boiling points due to the greater number of London forces that they contain* branching lowers the boiling point though

Question 53

alkanes and cycloalkanes solubility in water

Answer 53

are insoluble in water because of their low polarity and inability to make hydrogen bonds *least dense of all groups of organic compounds*

Question 54

conformations + conformer

Answer 54

**conformations**: temporary molecular shapes that result from a rotation about a single bond **conformer**: each possible structure of conformation

Question 55

how to draw Newman projections

Answer 55

the circle represents the back carbon, the 3 lines represent the front carbon **looking from the left**: atom on the wedge is on the RIGHT side of Newman projection - dash: on the left **looking from the right side**: atom on the wedge is on the LEFT side of the Newman projection - dash: on the right

Question 56

4 forms of Newman projections + their bond angles (b/w the 2 largest groups)

Answer 56

**staggered**: 2 types- anti and gauge **anti (180º)**: 2 largest groups are on polar ends, far apart, makes this the *most stable* b/c of least torsional strain **gauge (60º)**: still staggered but the groups are still apart, just not as much as anti **eclipsed (120º & 240º)**: kinda like the gauge staggered but eclipsed version **total eclipse (0º & 360º)**: when the 2 largest groups are directly behind each other **basically the closer the larger groups are together, the more repulsions and the less stable the molecule*

Question 57

stability of cycloalkanes (which is most stable and which is least)

Answer 57

**cyclohexane**: most stable cyclohexane (any more or less increases strain) - angle of 109.5º **cyclopropane**: least stable because so many strain (also the groups are closer together)

Question 58

4 types of conformations of cyclohexane & their relative stability

Answer 58

**chair**: most stable **twist boat**: more stable than boat but not as stable as chair **boat**: more stable than half-chair but still less stable than twist boat and chair **half chair**: least stable

Question 59

ring flip of cyclohexane

Answer 59

each carbon moves one down in the clockwise direction and axial groups become equatorial and equatorial groups become axial - molecule passes through the different conformations (twist boat and boat) before getting to the product

Question 60

equatorial/axial position stability

Answer 60

**most stable**: when both groups are in the equatorial position **least stable**: when both groups are in the axial position *2 groups*: more stable when the one where the bulkier group is in the equatorial position and the lighter one axial **the bigger the group, the less it wants to be in axial**

Question 61

1-3 biaxial interaction

Answer 61

clashes between groups in the 1 & 3 position that are both axial = torsional strain

Question 62

stability of chair conformations: cis and trans

Answer 62

**trans is more stable than cis** to determine cis and trans, only look at up and down NOT equatorial and axial

Question 63

cis and trans based on the wedges and dashes

Answer 63

both on wedge = cis both on dash = cis one on wedge, one on dash = trans

Question 64

catalytic hydrogenation (degree of unsaturation + IHD)

Answer 64

breaking of a **double/triple bond in alkanes by adding hydrogen to single bonds** - uses a metal catalyst like Pd, Pt, or Ni **triple bond = 2 H2 molecules needed** **double bond = 1 H2 molecule** *ring also counts as 1 degree of unsaturation*

Question 65

calculating IHD for compounds containing halogens, oxygen, or nitrogen

Answer 65

**halogen**: count halogen atoms as though they were hydrogen atoms (replace with H) **oxygen**: ignore oxygen atoms and calculate IHD from the remainder of the formula **nitrogen**: subtract 1 hydrogen for each nitrogen atom and ignore nitrogen atoms (I think this is if you use the formula though, but I dont use the formula to calculate it)

Question 66

which is a stronger nucleophile?

Answer 66

The one that can donate the electron pair more easily, so the one that’s less electronegative

Question 67

which is a stronger nucleophile?

Answer 67

The one that can donate the electron pair more easily, so the one that’s less electronegative