Organic Chemistry Alcohols and Ethers

Question 1

Alcohols are compounds with the general formula ROH. The ___ -OH is called the hydroxyl group. An alcohol can be thought of as a substituted water molecule, with an alkyl group R replacing one H atom

Answer 1

functional group

Question 2

An ___ is a compound with two alkyl or aryl groups bonded to a single oxygen atom. The general formula for an ether is R-O-R, and ethers can be thought of as disubstituted water molecules

Answer 2

ether

Question 3

Alcohols are named in the IUPAC system by replacing the -e ending of the root alkane with the ending -ol. The -OH group has high priority for naming; the carbon atom attached to the hydroxyl group usually must include in the longest chain and receive the lowest possible number. The common names for alcohols are given by naming the ___ group as a derivative, followed by the word alcohol

Answer 3

alkyl

Question 4

___ of the general formula ArOH, with a hydroxyl group attached to an aromatic ring, are called phenols

Answer 4

compounds

Question 5

___ have a hydrogen attached directly to an oxygen, and thus are able to form hydrogen bonds. As a result of these strong intermolecular attractions, the boiling points of alcohols are significantly higher than those of their analogous hydrocarbons

Answer 5

alcohols

Question 6

The ___ of the hydroxyl group is weakly acidic, and alcohols can dissociate into protons and alkoxy ions just as water dissociates into protons and hydroxide ions. pK sub a values of several compounds are listed below. The presence of electron withdrawing groups such as fluorine stabilize the negatively charged conjugate base of the alcohol, thus decreasing the pK sub a. Conversely, alkyl groups destabilize the anionic form because of their electron donating properties, thereby increasing the pK sub a.

Answer 6

hydrogen atom

Question 7

Phenols are more acidic than ___ alcohols, due to resonance structures that distribute the negative charge of the conjugate base throughout the ring, thus stabilizing the anion. This acidity allows phenols to readily form salts with inorganic bases such as Na OH. Phenols readily form intermolecular hydrogen bonds and have relatively high melting and boiling points. However phenol and many of its derivatives are only slightly soluble n water due to the conflicting effects of the hydrophobicity of the phenyl ring and the ability of the -OH group to hydrogen bond. The presence of other substituents on the ring has significant effects on the acidity, boiling point, and melting point of phenols. As with other aromatic compounds, electron-withdrawing substituents increase acidity by stabilizing the negatively charged conjugate base, and electron-donating groups decrease acidity

Answer 7

aliphatic

Question 8

1. SN1 and SN2 ___ to create alcohols. Conversely, protonation of an alcohol allows it to act as a leaving group in these reactions
2. Electrophilic addition of water to a double bond to create an alcohol. Conversely, elimination reactions (E1, E2) remove hydroxyls to create a double bond.
3. Nucleophilic addition to a carbonyl to create an alcohol
4. Oxidation and reduction: alcohols are at the most reduced end of the oxidation-reduction continuum as they have only single bonds to oxygen. carbonyl-containing compounds are more oxidized, as demonstrated by the larger number of bonds to oxygen from a single carbon

Answer 8

nucleophilic substitution

Question 9

___ can be prepared from the reduction of aldehydes, ketones, carboxylic acids, or esters. Lithium aluminum hydride (LiAlH4, or LAH) and sodium borohydride (NaBH4) are the two most frequently used reducing reagents. LAH is stronger and less specific, whereas NaBH4 is milder and more selective. Both LAH and NaBH4, however, will reduce aldehydes and ketones to alcohols

Answer 9

alcohols

Question 10

___ may be synthesized from arylsulfonic acids with heat and NaOH However, this reaction is useful only for phenol or its alkylated derivatives, as most functional groups are destroyed by the harsh reaction conditions.
A more versatile method of synthesizing phenols proceeds using hydrolysis of diazonium salts

Answer 10

phenols

Question 11

___ can be dehydrated in strongly acidic solution (usually H2SO4) to produce alkenes. The mechanism of this dehydration reaction is E1, and proceeds by first protonating the alcohol and then removing a water molecule to form the double bond.
Notice that two products are obtained, with the more stable alkene being the major product. This occurs via movement of a proton to produce the more stable secondary carbocation. This type of rearrangement is commonly encountered with carbocations

Answer 11

alcohols

Question 12

The direct displacement of ___ groups in substitution reaction is rare because the hydroxide ion is a poor leaving group. However, the hydroxyl group can be converted to a good leaving group using two different approaches. Protonating the alcohol makes water the leaving group, which works well for SN1 reactions. Alternatively, the alcohol can be converted into a tosylate (p-toluenesulfonate) group, which is an excellent leaving group for SN2 reactions

Answer 12

hydroxyl

Question 13

Another ___ reaction that serves as a common method of converting alcohols into alkyl halides is through the formation of inorganic esters, which then readily undergo SN2 reactions. Alcohols react with thionyl chloride to produce a chlorosulfite intermediate and HCl. The chloride ion of HCl then displaces SO2 and regenerates Cl-, forming the desired alkyl chloride.
An analogous reaction in which the alcohol is treated with PBr3 instead of thionyl chloride produces alkyl bromides.
Phenols readily undergo electrophilic aromatic substitution reactions. Because -OH group of phenol has lone pairs that can be donated to the ring, the -OH is a strongly activating, ortho/para-directing ring substituent

Answer 13

substitution

Question 14

The ___ of alcohols generally involves a metal oxidizing agent such as chromium or manganese. PCC is commonly used as a mild oxidant. It converts primary alcohols to aldehydes but does not continue the oxidation to the carboxylic acid. PCC can also be used to convert a secondary alcohol to a ketone. Potassium permanganate (KMNO4) is a very strong oxidizing agent that will react with primary alcohol to create a carboxylic acid or with a secondary alcohol to create a ketone. Another reagent used to oxidize primary or secondary alcohols is alkali (either sodium or potassium) dichromate salt

Answer 14

oxidation

Question 15

A stronger oxidant is chromium trioxide, CrO3. This is often dissolved with dilute sulfuric acid in acetone; the mixture is called ___. It oxidizes primary alcohols to carboxylic acids and secondary alcohols to ketones

Answer 15

jones reagent

Question 16

___ cannot be oxidized as the carbon-carbon bonds are resistant to oxidizing agents, and therefore no second bond to the oxygen can be created

Answer 16

tertiary alcohols

Question 17

Treatment of ___ with oxidizing reagents produces compounds called quinones 2,5-cyclo-hexadiene-1,4-diones

Answer 17

phenols

Question 18

An ___ is a compound with two alkyl (or aryl) groups bonded to an oxygen atom. The general formula for an ether is ROR. Ethers can be thought of as disubstituted water molecules. The most familiar ether is diethyl ether, once used as a medical anesthetic.

Answer 18

ether

Question 19

Ethers named according to IUPAC rules as ___, with the smaller chain as the prefix and the larger chain as the suffix. There is a common system of nomenclature in which ethers are named as alkyl alkyl ethers. In this system, methoxyethane would be named ethyl methyl ether. The alkyl substituents are alphabetized

Answer 19

alkoxyalkanes

Question 20

Exceptions to these rules occur for cyclic ethers, also known as ___, for which many common names also exist such as oxirane (epoxide) and oxacyclopentane (tetrahydrofuran).

Answer 20

oxiranes

Question 21

___ do not undergo hydrogen bonding because they have no hydrogen atoms bonded to the ether oxygen atoms. Ethers therefore boil at relatively low temperatures compared to alcohols; in fact, they boil at approximately the same temperatures as alkanes of comparable molecular weight. Ethers are only slightly polar and therefore only slightly soluble in water. They are relatively inert to most organic reagents and are frequently used as solvents. However, ethers can form highly reactive peroxides, requiring careful storage and handling

Answer 21

ethers

Question 22

Ethers are readily synthesized by the condensation of two molecules of an ___ in the presence of acid, producing a symmetrical ether and water in a substitution reaction.

Answer 22

alcohol

Question 23

The Williamson ether ___ produces asymmetrical ethers from the reaction of metal alkoxide ions with primary alkyl halides or tosylates. The alkoxides behave as nucleophiles and displace the halide or tosylate in an SN2 reaction, producing an ether.
Because this is an SN2 mechanism, alkoxides will attack only nonhindered halides. Thus, to synthesize a methyl ether, an alkoxide must attack a methyl halide; the reaction cannot be accomplished with the methoxide ion attacking a highly substituted alkyl halide substrate.

Answer 23

synthesis

Question 24

The Williamson ether synthesis can also be applied to phenols. Relatively mild reaction ___ are sufficient, due to the acidity of phenols

Answer 24

conditions

Question 25

___, also known as oxiranes, are prepared in a number of ways. Oxiranes can be synthesized by means of an internal SN2 displacement. Since the nucleophile and substrate are part of the same molecule, they are in close proximity, facilitating the reaction

Answer 25

cyclic ethers

Question 26

Oxidation of an ___ with a peroxy acid (general formula RCOOOH) such as mCPBA (m-chloroperoxybenzoic acid) will also produce an oxirane

Answer 26

alkene

Question 27

Ethers react with the oxygen in air to form highly explosive compounds called ___ (general formula ROOR). For this reason, ethers are typically stored at low temperature and away from light

Answer 27

peroxides

Question 28

___ of straight-chain ethers will take place only under vigorous conditions: usually at high temperatures in the presence of HBr or HI. Cleavage is initiated by protonation of the ether oxygen. The reaction then proceeds by an SN1 or SN2 mechanism, depending on the conditions and the structure of the ether . The alcohol products usually react with a second molecule of hydrogen halide to produce a second alkyl halide

Answer 28

cleavage

Question 29

The same basic principles and reaction mechanisms of substitution reactions apply to ___. Since epoxides are highly strained cyclic ethers, they are susceptible to SN2 reactions. Unlike straight-chain ethers, these reactions can be catalyzed by acids or bases. In symmetrical epoxides, either carbon can be attacked by a nucleophile; however, in asymmetrical epoxides, the most substituted carbon is attacked by the nucleophile in the presence of acid, and the least substituted carbon is attacked in the presence of base
Reactions of epoxides provide additional insight into SN1 and SN2 reaction mechanisms. Base-catalyzed cleavage of epoxides has the most SN2 character, so it occurs at the least hindered (least substituted) carbon. The basic environment provides the strong nucleophile required for SN2 reactions. In contrast, acid-catalyzed cleavage is thought to have some SN1 character as well as some SN2 character. The epoxide oxygen can be protonated, making it a better leaving group. This gives the carbons partial positive charges. Since substitution stabilizes this charge (tertiary carbons provide the most stable carbocations), the more substituted C becomes a good target for nucleophilic attack

Answer 29

epoxides