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9,10,11,12,13 Flashcards

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1
Q
A

Acetylene
“Acet-“: This prefix is related to the two-carbon unit found in the molecule. It stems from the Latin word “acetum,” meaning “vinegar.” This connection arises because acetic acid (the main component of vinegar) can be produced from acetylene through a series of chemical reactions.
“-ylene”: This suffix is the standard ending used to denote alkynes in chemical nomenclature. It signifies the presence of the carbon-carbon triple bond, which is the defining characteristic of this class of compounds.

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2
Q
A

Acetylide ion
- “ide” indicates the presence of a negative charge

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3
Q
A

Alkynide ion

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4
Q

True or False:
The conjugate base of a terminal alkyne, called an alkynide ion, can only be formed with a sufficiently
strong base.

A

True

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5
Q

Strong bases that can deprotonate acetylene or terminal alkyne

A
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6
Q

________ dihalide, which means that both halogens are con-
nected to the same carbon atom.

A

geminal

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7
Q

________ dihalide, which the two halogens are connected to adjacent carbon atoms:

A

vicinal

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8
Q

A poisoned catalyst will catalyze the conversion of an alkyne into a _______ alkene, but it will not catalyze the subsequent reduction to form the alkane

A

cis

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9
Q

Examples of _______________________
- Lindlar’s catalyst, which is a Pd catalyst prepared with CaCO3 and traces of PbO2.
- P-2 catalyst, which is nickel- boron complex (Ni2B).

A

poisoned catalysts

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10
Q

Alkynes can also be reduced to trans alkenes via a reaction called _________________________

A

dissolving metal reduction

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11
Q

To produce a _________ alkene, an Alkyne can be treated with sodium metal in liquid ammonia.

A

trans

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12
Q

When the starting alkyne is treated with excess H-X, two successive addition reactions occur, producing a ______________

A

geminal dihalide

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13
Q

In the presence of peroxides, HBr undergoes an _______________ addition across an alkene or terminal alkyne

A

anti-Markovnikov
*peroxides causes radical addition mechanism
Radical addition only occurs with HBr (not with HCl or HI)

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14
Q

In the context of alkynes, hydration (addition of OH & H) results in the formation of an______, which then tautomerizes to a ketone or aldehyde

A

enol

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15
Q

Hydration of Alkynes
Step 1: Addition of Water: Water adds across the triple bond in the presence of a strong acid catalyst (usually sulfuric acid, H2SO4) and mercury(II) sulfate (HgSO4).
Step 2: Tautomerization: The enol intermediate rapidly converts to a more stable ketone or aldehyde through a process called tautomerization.
*The regioselectivity of the reaction is governed by Markovnikov’s rule

A

Hydration of alkynes is a valuable synthetic tool for preparing ketones and aldehydes

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16
Q

Hydration of internal alkynes generally yields _________

A

ketones

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17
Q

Hydration of terminal alkynes produces ____________

A

aldehydes

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18
Q

The initial product of alkyne hydration is an enol, which quickly_____________ to the more stable carbonyl compound (ketone or aldehyde).

A

tautomerizes
H on the O relocates

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19
Q

The enol and ketone are said to be ____________, which are constitutional isomers that rapidly interconvert via the migration of a H

A

tautomers
- tautomers are constitutional isomers that exist in equilibrium with one another. Once the equilibrium has been reached, the concentrations of ketone and enol can be measured. In contrast, resonance structures are not different compounds and they are not in equilibrium with one another.

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20
Q

interconversion between an enol and a ketone is called _______________

A

keto-enol tautomerization

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21
Q

True or False:
Tautomerization cannot be prevented, and it is catalyzed by either acid or base.

A

True

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22
Q

An alkyne possesses 2 pi bonds. As a result, two molecules of BH3 can add across the alkyne. To prevent the second addition, a
dialkyl borane (R2BH) is employed instead of BH3. The two alkyl groups provide______________ that prevents the second addition.
2 commonly used dialkyl boranes are disiamylborane and 9-BBN

A

steric hindrance

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23
Q

Hydroboration- Oxidation of Alkynes, the initial product of this reaction is an enol that cannot be isolated because it is rapidly converted into an____________ via tautomerization.

A

aldehyde

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24
Q

Halogenation of Alkynes, excess or 2 equivalents of Br2 or Cl2 will add to form a ____________

A

tetrahalide

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25
Q

Halogenation of Alkynes, 1 equivalent of Br2 or Cl2 will add to form a ____________

A

dihalide
- E isomer (opposite sides due to anti addition)

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26
Q

When treated with ozone followed by water, Alkynes undergo oxidative-cleavage to produce ____________

A

carboxylic acids

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27
Q

When a terminal Alkyne undergoes oxidative-cleavage, the terminal carbon atom is converted into __________

A

carbon dioxide

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28
Q

What type of reaction does the acetylide ion undergo with a primary alkyl halide?

A

SN2 rxn

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29
Q

What type of reaction does the acetylide ion undergo with a secondary or tertiary alkyl halide?

A

E2

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30
Q

A terminal alkyne can be deprotonated by a strong base, such as sodium amide (NaNH2), the resulting alkynide ion can function as a nucleophile when treated with an alkyl halide and this transformation proceeds via an SN2 pathway and provides a method to install an alkyl group. This process is called __________ of Terminal Alkynes

A

Alkylation of terminal alkynes
*This process is only efficient with methyl or primary alkyl halides (SN2)

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31
Q

Acetylene possesses two terminal protons (one on either side) and can therefore undergo alkylation _________

A

twice

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32
Q

What is the stability trend for alkyl radicals?

A

Tertiary > Secondary > Primary > Methyl

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33
Q

What are some common reactions involving radicals?

A

Halogenation, addition reactions, and polymerization.

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34
Q

Are radicals electrophilic or nucleophilic?

A

Electrophilic due to their electron deficiency.

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35
Q

Is a carbon radical trigonal planar, trigonal pyramidal, or in-between the two?

A

A carbon radical is between these two cases, because it has one nonbonding electron. It therefore might seem reasonable to expect that the geometry of a carbon radical would be somewhere in between trigonal planar and trigonal pyramidal. Experiments suggest that carbon radicals either are trigonal planar or exhibit a very shallow pyramid (nearly planar) with a very low barrier to inversion
TREATED AS TRIGONAL PLANAR

36
Q

What factors contribute to radical stability?

A

Hyperconjugation and inductive effects.

37
Q

Order of stability of radicals?
Tertiary vs Allylic vs Benzylic

A

Benzylic > Allylic > Tertiary

38
Q

There are six different kinds of arrow-pushing patterns that comprise radical reactions.
1.
2.
3.
4.
5.
6.

A

Homolytic cleavage
Addition to a π bond
Hydrogen abstraction
Halogen abstraction
Elimination
Coupling

39
Q

__________ cleavage requires a large input of energy. This energy can be
supplied in the form of heat (Δ) or light (hν).

A

Homolytic cleavage
*initiation step in radical reaction

40
Q

A radical adds to a π bond, thereby destroying the π bond and generating a new radical.

A

Addition to a pi bond
*a propagation step in radical reaction

41
Q

A radical can abstract a hydrogen atom from a compound, generating a new radical. Don’t confuse this step with a proton transfer, which is an ionic step. In a proton transfer, only the nucleus of the hydrogen atom (a proton, H+) is being transferred. Here, the entire hydrogen atom (proton and electron, H*) is being transferred from one location to another.

A

Hydrogen abstraction
*a propagation step in radical reaction

42
Q

A radical can abstract a halogen atom, generating a new radical. This step is similar to hydrogen abstraction, only a halogen atom is being abstracted instead of a hydrogen atom.

A

Halogen abstraction
*a propagation step in radical reaction

43
Q

The position bearing the unpaired electron is called the alpha position. In an elimination step, a double bond forms between the alpha (α) and beta (β) positions. As a result, a single bond at the β position is cleaved, causing the compound to fragment into two pieces.

A

Elimination
*a propagation step in radical reaction

44
Q

Two radicals join together and form a bond.

A

Coupling
*termination step in radical reaction

45
Q

The step when radicals are created

A

Initiation step

46
Q

The step when two radicals annihilate each other by forming a bond.

A

Termination step

47
Q

2 important notes in the Propagation step of a radical reaction

A
  1. Formation of the products
  2. Regeneration of the radical
48
Q

The first propagation step is a ____________ abstraction, and the second propagation
step is a ______________ abstraction.

A

hydrogen
halogen

49
Q

In radical reactions, the sum of the ____________ steps gives the net chemical reaction.

A

propagation

50
Q

Radical reaction (chlorination)
In order to produce monohalogenation, there needs to be a low concentration of the _____________

A

halogen
- excess halogen leads to polyhalogenation

51
Q

Photochemical initiation requires the use of UV light, while thermal initiation requires a very high temperature (several hundred degrees Celsius) in order to produce the energy necessary to cause homolytic bond cleavage of a Cl-Cl bond. Achieving thermal initiation at more ‘moderate temperatures’ requires the use of a _______________, a compound with a weak bond that undergoes homolytic bond cleavage with greater ease.

A

radical initiator
- Alkyl peroxides
- Acyl peroxides

52
Q

A_______________ is a compound that prevents a chain process from either getting started or continuing and they effectively destroy radicals

A

radical inhibitor (radical scavenger)
- O2
- hydroquinone

53
Q

What is the trend of halogen reactivity in radical halogenation reactions?

A

Fluorine > Chlorine > Bromine > Iodine

54
Q

What is the rate-determining step in a radical reaction?

A

The hydrogen abstraction sep of propagation

55
Q

Radical reaction:
Why does bromination show greater ‘selectivity’ than chlorination?

A

The transition state for bromination is closer to the product (radical) in energy, making radical stability a more important factor in determining the reaction rate.

56
Q

What is the relative reactivity of chlorine and bromine towards different types of hydrogen atoms?

A

Chlorine is less selective than bromine. It shows a smaller difference in reactivity between primary, secondary, and tertiary hydrogens.

57
Q

What is the stereochemical outcome of radical halogenation at a chiral center?

A

Radical halogenation at a chiral center leads to a racemic mixture of products.
This is because the intermediate radical is planar, and the halogen can attack from either face with equal probability.

58
Q

If there is an existing chiral center that is not involved in the radical halogenation
process. In such a case, the products are _______________, rather than enantiomers

A

diastereomers

59
Q

What is radical allylic bromination of an alkene?

A

The substitution of a hydrogen atom at the allylic position with a bromine atom using N-bromosuccinimide (NBS).
- be careful high concentrations of Br2 will add across double bond instead

60
Q

What is the one serious flaw with radical allylic bromination of an alkene?

A

When the reaction is performed with Br2 as the reagent, a competition occurs between allylic bromination and ionic addition of bromine across the π bond
so to avoid this competing reaction, the concentration of bromine (Br2) must be kept as low as possible throughout the reaction. This can be accomplished by using N-bromosuccinimide (NBS) as a reagent, instead of Br2

61
Q

_____________ can rise into the stratosphere, where they are broken down by UV light, releasing chlorine radicals. These chlorine radicals can catalyze the destruction of ozone, disrupting the Chapman cycle and leading to ozone depletion.

A

CFCs
- The Montreal Protocol is an international treaty designed to phase out the production and use of ozone-depleting substances, including CFCs

62
Q

What are some alternatives to CFCs?

A

Some alternatives to CFCs include hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluoro-olefins (HFOs).
- UV light can’t homolytically cleave a C-F bond

63
Q

Ultimately, the ozone cycle in the stratosphere turns harmful UV radiation into __________, another form of energy

A

Heat

64
Q

In the presence of atmospheric oxygen, organic compounds are known to undergo a slow oxidation process called ___________________

A

autooxidation

65
Q

Naturally occurring fats and oils, such as vegetable oil, are generally mixtures of compounds called triglycerides, which contain three long hydrocarbon chains. The hydrocarbon chains often contain double bonds, which render them susceptible to_________________, specifically at the allylic positions where hydrogen abstraction can occur more readily. The resulting hydroperoxides contribute to the rancid smell that develops over time in foods containing unsaturated oils. Moreover, hydroperoxides are also toxic. Food products with unsaturated oils therefore have a short shelf life unless radical inhibitors are used to slow the autooxidation process. Many radical inhibitors are used as food preservatives, including BHT and BHA (antioxidants). Naturally occurring antioxidants are vitamin C & vitamin E.

A

autooxidation

66
Q

What is the key difference between radical addition of HBr and regular HBr addition to alkenes?

A

Radical addition follows Anti-Markovnikov regioselectivity, while regular addition follows Markovnikov’s rule.

67
Q

What conditions are necessary for radical addition of HBr?

A

Presence of peroxides (like ROOR) or other radical initiators.

68
Q

What are some common polymers produced by radical polymerization?

A

Polyethylene, polystyrene, PVC, and Teflon.

69
Q

How does the polymer chain grow?

A

Through the continuous addition of monomer units to the active radical chain end.

70
Q

Most synthesis problems will have numerous correct answers,
although_______________ should always be a top priority (fewer
steps are preferable).

A

efficiency

71
Q

What is the IUPAC nomenclature for alcohols?

A

Replace the -e ending of the parent alkane with -ol (e.g., methane becomes methanol).

72
Q

How are the common names of alcohols formed?

A

Name the alkyl group followed by the word “alcohol” (e.g., methyl alcohol).

73
Q

What are the products when an alcohol acts as an acid?

A

An alkoxide ion (RO-) and a proton (H+)

74
Q

How does alkyl substitution influence alcohol acidity?

A

Increased alkyl substitution decreases acidity. Tertiary alcohols are less acidic than secondary, which are less acidic than primary.

75
Q

What is the functional group of a phenol?

A

A hydroxyl group (-OH) connected to a benzene ring.

76
Q

Compare the acidity of phenols and alcohols.

A

Phenols (pKa around 10) are significantly more acidic than alcohols.
- the phenoxide ion (conjugate base) is stabilized by resonance delocalization of the negative charge into the benzene ring.

77
Q

Alcohols can be prepared by substitution reactions in which a leaving group
is replaced by a hydroxyl group. A primary substrate will require _______ conditions (a strong nucleophile), while a tertiary substrate will require _______ conditions (a weak nucleophile).

A

SN2
SN1
- For a secondary substrate, neither SN2 or SN1 is effective for preparing a secondary
alcohol (under SN1 conditions, the reaction is generally too slow & SN2 conditions will generally favor elimination over substitution)

78
Q

Alcohols can be prepared by addition reactions via ____________, ____________, & ____________

A

Acid-Catalyzed Hydration (markovnikov but possible C+ rearrange)
Oxymercuration-demercuration (markovnikov & anti-addition)
Hydroboration-oxidation (anti-markovnikov & syn-addition)

79
Q

Assigning Oxidation States:
We treat all bonds as if they were purely ionic, and we break them heterolytically, giving each pair of electrons to the more _________________ atom in each case.

A

electronegative

80
Q

What are the two main functional groups that can be reduced to form alcohols?

A

Aldehydes and ketones

81
Q

What are the two common reducing agents used to prepare alcohols from aldehydes and ketones?

A

Sodium borohydride (NaBH4) and lithium aluminum hydride (LiAlH4)
- can undergo hydrogenation in the presence of a metal
catalyst although more forcing conditions are generally required (higher temperature and pressure), so this method is rarely used by synthetic chemists.

82
Q

Compare the reactivity of NaBH4 and LiAlH4.

A

LiAlH4 is a stronger reducing agent than NaBH4. LiAlH4 can reduce a wider range of functional groups, including carboxylic acids and esters, while NaBH4 is more selective for aldehydes and ketones.

83
Q

Diols can be prepared from diketones via reduction using _____________ any of the reducing agents

A

2 equivalents

84
Q

Diols can also be made via __________________ of an alkene.

A

anti or syn dihydroxylation

85
Q
A

Organic Chem Class (9 decks)

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