Dehydration Reactions of Alcohols
54 Questions
1 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is required for an alcohol to undergo nucleophilic substitution?

  • High temperature
  • Increased pH levels
  • Presence of a good leaving group (correct)
  • Low concentration of reactants

Dehydration of alcohols typically involves the use of acids like hydrochloric acid.

False (B)

What is the primary mechanism of dehydration for secondary and tertiary alcohols?

E1 mechanism

The __________ rule states that the more substituted alkene is the major product in dehydration reactions.

<p>Zaitsev</p> Signup and view all the answers

Match the type of alcohol with its corresponding dehydration mechanism:

<p>1° alcohol = SN1 mechanism 2° alcohol = E1 mechanism 3° alcohol = E1 mechanism</p> Signup and view all the answers

Which statement is true regarding 1° alcohols?

<p>They undergo dehydration by an E2 mechanism. (A)</p> Signup and view all the answers

Entropy favors product formation during dehydration reactions.

<p>True (A)</p> Signup and view all the answers

What is the effect of bond strength on the enthalpy favorability in dehydration reactions?

<p>The σ bonds broken are stronger than the σ and π bonds formed.</p> Signup and view all the answers

What is a common example of a cyclic ether?

<p>Tetrahydrofuran (THF) (D)</p> Signup and view all the answers

Epoxides can only be named using epoxyalkanes.

<p>False (B)</p> Signup and view all the answers

What type of interactions do alcohols, ethers, and epoxides exhibit due to their structure?

<p>Dipole-dipole interactions</p> Signup and view all the answers

Epoxides are often prepared by adding an O atom to an ________.

<p>alkene</p> Signup and view all the answers

Match the following naming conventions with their descriptions:

<p>Epoxyalkanes = Naming as a substituent using alkane chain Oxiranes = Naming as derivatives of a ring with oxygen Alkene oxides = Naming by replacing epoxide oxygen with a double bond</p> Signup and view all the answers

What is the preferred method to prepare an unsymmetrical ether?

<p>Williamson ether synthesis (C)</p> Signup and view all the answers

Alcohols are more polar than ethers and epoxides due to their capability for hydrogen bonding.

<p>True (A)</p> Signup and view all the answers

What by-product is produced when sodium ethoxide is formed from ethanol and NaH?

<p>Hydrogen gas (H2)</p> Signup and view all the answers

What is the purpose of using SOCl2 in the conversion of alcohols?

<p>To convert alcohols into alkyl chlorides (D)</p> Signup and view all the answers

PBr3 is used to convert primary and secondary alcohols into alkyl bromides.

<p>True (A)</p> Signup and view all the answers

What byproducts are formed when a 1° or 2° alcohol is treated with SOCl2 and pyridine?

<p>HCl and SO2</p> Signup and view all the answers

The alkyl tosylate is formed from alcohol and _______, a reagent used to convert alcohols into good leaving groups.

<p>p-toluenesulfonyl chloride</p> Signup and view all the answers

Match the following reagents with their corresponding products:

<p>SOCl2 = Alkyl Chloride PBr3 = Alkyl Bromide TsCl = Alkyl Tosylate Br¯ = Nucleophile for substitution</p> Signup and view all the answers

What happens to the stereochemistry when (S)-2-butanol is converted to its tosylate?

<p>The configuration is retained (B)</p> Signup and view all the answers

The tosylate group is a poor leaving group due to its high pKa.

<p>False (B)</p> Signup and view all the answers

What are the two parts of the mechanism for alcohol conversion using SOCl2?

<p>Conversion of the OH group into a better leaving group and nucleophilic cleavage by Cl¯.</p> Signup and view all the answers

What mechanism leads to inversion of configuration when an SN2 reaction occurs?

<p>Inversion of stereochemistry (C)</p> Signup and view all the answers

The reaction of an alcohol with TsCl and pyridine results in a retention of configuration.

<p>True (A)</p> Signup and view all the answers

What are the two strong acids mentioned that can convert a poor leaving group in ethers into a good leaving group?

<p>HBr and HI</p> Signup and view all the answers

In the reaction of ethers with strong acids, the C—O bonds are cleaved, resulting in two __________.

<p>alkyl halides</p> Signup and view all the answers

Match the following reactions with their corresponding mechanisms:

<p>Ethers with HI = SN1 mechanism Ethers with HBr = SN2 mechanism Alcohol to tosylate = Retention of configuration Alcohol to substitution product = Inversion of configuration</p> Signup and view all the answers

What happens to the configuration of a stereogenic center after reaction with TsCl followed by nucleophilic attack?

<p>It undergoes inversion (B)</p> Signup and view all the answers

Epoxides contain a good leaving group, making them reactive with nucleophiles.

<p>False (B)</p> Signup and view all the answers

What is the effect of a strong nucleophile or acid on the epoxide structure?

<p>Opens the strained three-membered ring</p> Signup and view all the answers

What type of mechanism do strong nucleophiles use to open an epoxide ring?

<p>SN2 mechanism (B)</p> Signup and view all the answers

The reaction of 1,2-epoxycyclohexane with ¯OCH3 always produces a single enantiomer.

<p>False (B)</p> Signup and view all the answers

Name one common nucleophile that can open an epoxide ring.

<p>¯OH</p> Signup and view all the answers

The nucleophile attacks an electron-deficient carbon in the first step, cleaving the ______ bond.

<p>C—O</p> Signup and view all the answers

Match the following acids to their ability to open epoxide rings:

<p>HCl = Can open epoxide rings HBr = Can open epoxide rings HI = Can open epoxide rings H2O = Can open epoxide rings</p> Signup and view all the answers

What is formed when the alkoxide from an epoxide ring opening is protonated?

<p>A neutral product with two functional groups (C)</p> Signup and view all the answers

Optically inactive starting materials can produce optically active products.

<p>False (B)</p> Signup and view all the answers

What type of carbon do alcohols contain the OH group bonded to?

<p>saturated carbon (sp3)</p> Signup and view all the answers

What suffix indicates the presence of a hydroxyl group in a compound's name?

<p>-ol (C)</p> Signup and view all the answers

Phenols are less acidic than alcohols due to their resonance stabilization.

<p>False (B)</p> Signup and view all the answers

What is the result of protonation of alcohols by strong acids?

<p>Oxonium ions are formed.</p> Signup and view all the answers

The _____cidity const______nt, K, me______sures the extent to which ______ Brønsted ______cid tr______nsfers ______ proton to w______ter.

<p>a</p> Signup and view all the answers

Match the type of alcohol with its boiling point characteristics:

<p>Primary Alcohol = Higher boiling point than alkanes Secondary Alcohol = Higher boiling point than alkanes Tertiary Alcohol = Generally the highest boiling point Methyl Alcohol = Lowest boiling point among alcohols</p> Signup and view all the answers

Which factor makes an alkoxide ion formation energetically favored?

<p>Solvation by water (A)</p> Signup and view all the answers

What is the general product formed by the reduction of carbonyl compounds?

<p>An alcohol.</p> Signup and view all the answers

Grignard reagents can add to carboxylic acids.

<p>False (B)</p> Signup and view all the answers

Phenols are much more acidic than alcohols due to __________ stabilization of the phenoxide ion.

<p>resonance</p> Signup and view all the answers

Match the oxidation reagent with its corresponding alcohol reaction:

<p>KMnO4 = Can oxidize primary alcohols PCC = Oxidizes primary alcohols to aldehydes Na2Cr2O7 = Used for secondary alcohols LiAlH4 = Not effective for oxidations</p> Signup and view all the answers

Which of the following factors influences the acidity of alcohols?

<p>Steric effects (D)</p> Signup and view all the answers

What is the role of tosylates in reactions involving alcohols?

<p>Tosylates are converted into alkyl halides through nucleophilic substitution.</p> Signup and view all the answers

Secondary alcohols dehydrate more easily than tertiary alcohols.

<p>False (B)</p> Signup and view all the answers

Reduction of aldehydes produces __________ alcohols.

<p>primary</p> Signup and view all the answers

Flashcards

Cyclic Ethers

Cyclic ethers contain an oxygen atom within the ring structure.

Epoxide Nomenclature (epoxyalkane)

Epoxides named as epoxyalkanes use the prefix "epoxy" and two numbers specifying the carbons bonded to the oxygen.

Epoxide Nomenclature (oxirane)

Epoxides can also be named as oxiranes; the O is always at position 1 in the numbering.

Epoxide Nomenclature (alkene oxide)

Epoxides are also named as alkene oxides; replace the oxygen with a double bond to get the alkene parent.

Signup and view all the flashcards

Alcohols vs Ethers vs Epoxides (polarity)

Alcohols are more polar due to intermolecular hydrogen bonds, while ethers and epoxides are less polar due to dipole-dipole interactions.

Signup and view all the flashcards

Williamson Ether Synthesis

A common way to make ethers where an alkoxide salt reacts in an SN2 reaction.

Signup and view all the flashcards

Halohydrins

Organic compounds with both a hydroxy group and a halogen atom on adjacent carbons.

Signup and view all the flashcards

Epoxide Formation (halohydrins)

Epoxides can be formed from halohydrins through an intramolecular Williamson ether synthesis.

Signup and view all the flashcards

Alcohol Dehydration

A chemical reaction where the elements of water (OH and H) are removed from an alcohol, creating an alkene.

Signup and view all the flashcards

Mechanism of 1° Alcohol Dehydration

1° Alcohols undergo alkene formation through an E2 mechanism, as the intermediate carbocation is unstable, making E1 impossible.

Signup and view all the flashcards

Dehydration Reaction Conditions

Acidic conditions such as H2SO4 or TsOH, or phosphorus oxychloride (POCl3) with an amine base are used to dehydrate alcohols.

Signup and view all the flashcards

Zaitsev's Rule in Dehydration

When possible, dehydration reactions prefer creating the more substituted alkene, according to the principle.

Signup and view all the flashcards

E1 Mechanism in Dehydration

Secondary and tertiary alcohols primarily react to form alkenes using an E1 mechanism, leading to clean elimination via carbocation intermediate.

Signup and view all the flashcards

E2 Mechanism

Primary alcohols typically follow an E2 reaction mechanism during dehydration.

Signup and view all the flashcards

Poor Leaving Group (OH)

The hydroxyl group (OH) in alcohols is not a good leaving group in nucleophilic substitution reactions.

Signup and view all the flashcards

Improved Leaving Group (H2O)

The OH group in alcohols can be converted to a better leaving group (water) through acid-catalyzed dehydration reactions.

Signup and view all the flashcards

ZnCl2 in Alcohol Reactions

Zinc chloride (ZnCl2) forms a complex with the oxygen atom of an alcohol, creating a good leaving group that facilitates SN2 reactions.

Signup and view all the flashcards

Stereochemistry and SN2

Understanding the mechanism of SN2 reactions allows us to predict the stereochemistry of products when the reaction occurs at a stereogenic center.

Signup and view all the flashcards

SOCl2 and PBr3 for Alkyl Halides

Primary and secondary alcohols can be converted to alkyl halides using thionyl chloride (SOCl2) for chlorides and phosphorus tribromide (PBr3) for bromides.

Signup and view all the flashcards

Conversion of OH to a Leaving Group

SOCl2 and PBr3 convert the hydroxyl group (OH) into a better leaving group in situ, allowing for nucleophilic displacement by Cl- or Br-.

Signup and view all the flashcards

Mechanism of SOCl2 Reaction

The reaction of a primary or secondary alcohol with SOCl2 and pyridine involves two steps: converting the OH group to a better leaving group and nucleophilic cleavage by Cl- via an SN2 reaction.

Signup and view all the flashcards

Mechanism of PBr3 Reaction

The reaction of a primary or secondary alcohol with PBr3 involves converting the OH group to a better leaving group and nucleophilic cleavage by Br- via an SN2 reaction.

Signup and view all the flashcards

Alkyl Tosylate

Alkyl tosylates are good leaving groups formed by reacting an alcohol with p-toluenesulfonyl chloride (TsCl) in the presence of pyridine.

Signup and view all the flashcards

Tosylates vs. Alkyl Halides

Alkyl tosylates, like alkyl halides, undergo nucleophilic substitution and elimination reactions. Tosylates are often treated with strong nucleophiles and bases, leading to SN2 and E2 mechanisms.

Signup and view all the flashcards

Epoxide Ring Opening

Epoxides are three-membered cyclic ethers that open with nucleophiles in a two-step process. The nucleophile attacks a strained C-O bond, relieving ring strain and forming an alkoxide. Then, the alkoxide is protonated to give a neutral product with two functional groups.

Signup and view all the flashcards

Epoxide Ring Opening Mechanism

Strong nucleophiles such as ¯OH, ¯OR, ¯CN, ¯SR, and NH3 open epoxides via an SN2 mechanism. Attack occurs from the backside of the epoxide, leading to inversion of configuration.

Signup and view all the flashcards

Epoxide Ring Opening Stereochemistry

Opening of an epoxide with a nucleophile can lead to a racemic mixture if the epoxide is symmetrical. Attacking from either side of the ring is equally likely, resulting in both enantiomers.

Signup and view all the flashcards

Epoxide Opening with Acids

Acids containing nucleophiles like HCl, HBr, HI, H2O, and ROH can also open epoxide rings. The mechanism is similar to nucleophile opening, but the acid protonates the oxygen first before nucleophilic attack.

Signup and view all the flashcards

Regioselectivity in Epoxide Opening

Opening an epoxide with either strong nucleophiles or acids is regioselective. This means one constitutional isomer is favored over the other. The regioselectivity depends on the nucleophile or acid used.

Signup and view all the flashcards

Alcohols

Alcohols contain an OH group bonded to a saturated carbon (sp3). They are important solvents and synthesis intermediates.

Signup and view all the flashcards

Phenols

Phenols contain an OH group directly attached to a carbon within an aromatic ring (benzene ring).

Signup and view all the flashcards

Enols

Enols have an OH group bonded to a vinylic carbon, which is sp2 hybridized.

Signup and view all the flashcards

Primary Alcohol

An alcohol where the carbon atom bonded to the hydroxyl group (OH) is also bonded to one other carbon atom and two hydrogen atoms.

Signup and view all the flashcards

Secondary Alcohol

An alcohol where the carbon atom bonded to the hydroxyl group (OH) is bonded to two other carbon atoms and one hydrogen atom.

Signup and view all the flashcards

Tertiary Alcohol

An alcohol where the carbon atom bonded to the hydroxyl group (OH) is bonded to three other carbon atoms and no hydrogen atoms.

Signup and view all the flashcards

Naming Alcohols

To name an alcohol, identify the longest carbon chain containing the OH group, replace the alkane ending with '-ol', and number the chain from the end nearest the OH.

Signup and view all the flashcards

Phenol Naming

Use 'phenol' as the parent name, not benzene. Substituents on the aromatic ring are named by their position from the OH group.

Signup and view all the flashcards

Alcohol Acidity

Alcohols are weak Brønsted acids, meaning they can donate a proton (H+) to water to a small extent. Alkyl groups make the alcohol a weaker acid.

Signup and view all the flashcards

Phenol Acidity

Phenols are more acidic than alcohols due to resonance in the phenoxide ion, which stabilizes the negative charge.

Signup and view all the flashcards

Alkoxide Formation

Alcohols react with strong bases (like NaH or NaNH2) to generate alkoxide ions. Alkoxides are used as reagents in organic chemistry.

Signup and view all the flashcards

Alcohol to Alkyl Halide

Alcohols can be converted to alkyl halides using reactions with HX (HCl or HBr) or SOCl2/PBr3.

Signup and view all the flashcards

Tosylation of Alcohols

Alcohols react with tosyl chloride (p-TosCl) in pyridine to form alkyl tosylates, which are good leaving groups.

Signup and view all the flashcards

Dehydration of Alcohols

Alcohols can be dehydrated to form alkenes, with the loss of OH and H from adjacent carbon atoms.

Signup and view all the flashcards

Acid-Catalyzed Dehydration

Tertiary alcohols are most easily dehydrated using acid (like H2SO4), while primary alcohols require harsh conditions.

Signup and view all the flashcards

Oxidation of Alcohols

Alcohols can be oxidized using reagents like KMnO4, CrO3, or Na2Cr2O7. Primary alcohols can be oxidized to aldehydes or carboxylic acids, while secondary alcohols form ketones.

Signup and view all the flashcards

Protecting Alcohols

Alcohols need to be protected from reacting with bases. This can be done by converting the hydroxyl group to a TMS ether, which can be easily removed later.

Signup and view all the flashcards

Tosylate Formation

Tosylates are formed by reacting an alcohol with TsCl (p-toluenesulfonyl chloride) in the presence of pyridine. This reaction proceeds with retention of configuration at a stereogenic center.

Signup and view all the flashcards

SN2 with Tosylates

The second step in converting an alcohol to a substitution product involves an SN2 reaction of the tosylate with a nucleophile. This step proceeds with inversion of configuration.

Signup and view all the flashcards

Ether Cleavage

Ethers can undergo substitution or elimination reactions, but their poor leaving group (oxygen) must first be converted to a better leaving group by reacting with strong acids (HBr or HI).

Signup and view all the flashcards

SN1 vs. SN2 in Ether Cleavage

The mechanism of ether cleavage depends on the structure of the alkyl groups attached to the oxygen. SN1 occurs with 2° or 3° alkyl groups, while SN2 occurs with methyl or 1° alkyl groups.

Signup and view all the flashcards

Epoxide Reactivity

Epoxides have a strained three-membered ring with two polar bonds, making them reactive despite lacking a good leaving group. Nucleophilic attack opens the ring and relieves strain.

Signup and view all the flashcards

Epoxide Opening Mechanism

Epoxide opening happens with strong nucleophiles or acidic conditions. The nucleophile attacks the strained C-O bond, leading to ring opening and formation of a new C-nucleophile bond.

Signup and view all the flashcards

Epoxide Reactions with Acids

Acids containing nucleophiles (HCl, HBr, HI, H2O, ROH) can open epoxide rings. The acid protonates the oxygen, making it a better leaving group, followed by nucleophile attack.

Signup and view all the flashcards

Study Notes

Alcohols, Ethers, and Epoxides

  • Alcohols contain a hydroxy group (OH) bonded to an sp³ hybridized carbon.
  • Ethers have two alkyl groups bonded to an oxygen atom.
  • Epoxides are ethers with an oxygen atom in a three-membered ring. They are also called oxiranes. The C-O-C bond angle is 60°, causing angle strain, making them more reactive than other ethers.
  • The oxygen atom in alcohols, ethers, and epoxides is sp³ hybridized. Alcohols and ethers have a bent shape similar to that of H₂O.
  • The bond angle around the O atom in an alcohol or ether is similar to the tetrahedral bond angle of 109.5°.
  • The C-O and O-H bonds are polar because the O atom is more electronegative than carbon or hydrogen.
  • Compounds with a hydroxy group on an sp² hybridized carbon, such as enols and phenols, undergo different reactions compared to alcohols.
  • Compounds with two hydroxy groups are called diols (or glycols). Compounds with three are called triols.

Nomenclature of Alcohols

  • Find the longest carbon chain containing the carbon connected to the OH group.
  • Change the -e ending of the parent alkane to -ol.
  • Number the chain to give the OH group the lowest possible number.
  • Name and number the substituents.

Nomenclature of Ethers

  • Name both alkyl groups bonded to the oxygen, arranging alphabetically.
  • Add the word "ether".
  • For symmetrical ethers, name the alkyl group and add "di-".

Nomenclature of Epoxides

  • Name the alkane chain or ring to which the O atom is bonded.
  • Use the prefix "epoxy" to name the epoxide.
  • Use two numbers to designate the location of carbons to which the O atoms are bonded.

Reactions of Alcohols

  • Alcohols are poor leaving groups.

  • To undergo a nucleophilic substitution reaction, the OH group must first be converted in to a good leaving group, such as H₂O, by using an acid like HCl.

  • Dehydration, a type of β elimination, involves the removal of the elements of OH- and H from adjacent atoms . This is typically carried out using strong acids or phosphorus oxychloride (POCI₃) in the presence of an amine base. -Typically using H₂SO₄ or p-toluenesulfonic acid (TsOH). -More substituted alcohols dehydrate more easily (1° < 2° < 3°). -Dehydration is regioselective and follows the Zaitsev rule -the more substituted alkene is the major product

Reactions of Ethers with Strong Acid

  • In order for ethers to undergo substitution or elimination reactions, their poor leaving group must be converted into a good leaving group by reaction with a strong acid like HBr or HI.
  • When ethers react with HBr or HI both C-O bonds are cleaved and two alkyl halides are formed as products.

Reactions of Epoxides

  • Epoxides are strained three-membered rings containing two polar bonds, and readily react with strong nucleophiles or acids.
  • Nucleophilic attacks open the ring, making it a favorable process even with a poor leaving group.

Carbocation Rearrangements

  • When carbocations are intermediates in reactions, a less stable carbocation can be converted into a more stable carbocation through a shift of a hydrogen or an alkyl group. This is called a rearrangement.
  • A 1,2-shift occurs when a migrating group moves with two bonding electrons.
  • 1,2-hydride shift - hydrogen atom movement
  • 1,2-alkyl shift - alkyl group movement

Conversion of Alcohols to Alkyl Halides

  • Substitution reactions do not occur with alcohols unless the OH group is converted into a good leaving group.
  • More substituted alcohols react more rapidly with HX(X=Cl, Br, I).
  • The mechanism of substitution reactions depend on the structure of the R group (methyl and 1°→S2; secondary and 3° → SN1).

Conversion of Alcohols into Alkyl Halides with SOCl₂ and PBr₃

  • Both reagents convert the OH group into a good leaving group directly in the reaction mixture.
  • Also provide the nucleophile (Chlorine or bromine) to displace the leaving group.

Tosylates

  • Alcohols can be converted into alkyl tosylates by treatment with p-toluenesulfonyl chloride (TsCl) and pyridine.
  • This process converts the poor leaving group (OH) to a good leaving group.

Reactions of Grignard Reagents with Carbonyl Compounds

  • Grignard reagents acts as nucleophilic carbon anions in adding to a carbonyl group.
  • The intermediate alkoxide is then protonated to yield the alcohol.

Oxidation of Alcohols

  • Alcohols can be oxidized by organic reagents such as potassium permanganate (KMnO4), chromium trioxide (CrO3), and sodium dichromate (Na2Cr2O7).
  • Sometimes more selective reagents such as pyridinium chlorochromate (PCC) are needed for sensitive alcohols.

Protection of Alcohols

  • Protecting groups can be used to temporarily modify reactive functional groups thus preventing undesired reactions.

1,2-Diols

  • Cis-1,2-diols form from hydroxylation of an alkene.
  • Trans-1,2-diols form from acid-catalyzed hydrolysis of epoxides.

Phenols

  • Contains an OH group connected to a carbon of a benzene ring
  • Weak Bronsted acids
  • Phenol is more acidic than typical alcohols

Additional Notes

  • The acidity constants (pKa) measure the extent to which a Brønsted acid transfers a proton to water.
  • Electron-withdrawing groups can stabilize the conjugate base (alkoxide) and lower the pKa.
  • Generally, alkyl groups make an alcohol a weaker acid; steric hindrance can also play a significant role.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

Alcohols, Ethers, and Epoxides (Chapter 7) PDF

Description

This quiz explores the mechanisms and conditions required for the dehydration of alcohols. It covers topics such as nucleophilic substitution, the role of acids, and the effects of bond strength and substitution on product formation. Test your understanding of alcohols, ethers, and epoxides in this comprehensive assessment.

More Like This

Dehydration &amp; Synthesis Reactions in Polymers
8 questions

Dehydration &amp; Synthesis Reactions in Polymers

SatisfyingTantalum avatar
SatisfyingTantalum
Dehydration Synthesis Flashcards
5 questions

Dehydration Synthesis Flashcards

AudibleFresno2256 avatar
AudibleFresno2256
Dehydration Reactions with Sugars
10 questions

Dehydration Reactions with Sugars

BriskPermutation avatar
BriskPermutation
Biology Experiment 3: Macromolecules
48 questions

Biology Experiment 3: Macromolecules

UnbiasedDramaticIrony avatar
UnbiasedDramaticIrony
Use Quizgecko on...
Browser
Open
Browser
Browser