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The defining characteristic of ethers is the presence of an ether functional group, wherein an oxygen atom covalently bridges two carbon atoms, represented by the general formula R–O–R′.
Answer: True
The fundamental structural motif of ethers involves an oxygen atom bonded to two organyl (alkyl or aryl) groups, yielding the general formula R–O–R′.
The C-O-C linkage within ethers typically deviates from linearity, exhibiting a bent geometry.
Answer: True
The C-O-C bond angle in ethers is not linear; for instance, in dimethyl ether, it is approximately 111 degrees, reflecting the sp3 hybridization of the oxygen atom and the presence of lone pairs.
According to valence bond theory, the oxygen atom in ethers is typically sp3 hybridized.
Answer: True
Valence bond theory posits that the oxygen atom in ethers, analogous to its hybridization in water and alcohols, is sp3 hybridized, accommodating two lone pairs of electrons and two sigma bonds to carbon atoms.
The alpha hydrogens adjacent to the ether oxygen atom exhibit greater acidity compared to those in simple hydrocarbons, owing to the inductive effect of the electronegative oxygen.
Answer: True
The electronegativity of the oxygen atom in ethers polarizes the adjacent C-H bonds, making the alpha hydrogens more susceptible to abstraction (i.e., more acidic) than those found in alkanes.
Alpha hydrogens in ethers are significantly more acidic than those found in carbonyl groups like ketones.
Answer: False
While alpha hydrogens in ethers are more acidic than those in simple hydrocarbons, they are significantly less acidic than the alpha hydrogens adjacent to carbonyl groups (ketones and aldehydes), due to the resonance stabilization of the enolate anion.
The ether linkage is not exclusively formed between carbon atoms; heavier Group 14 elements can also participate.
Answer: True
While carbon is the most common element forming ether linkages (C-O-C), analogous structures can be formed with other Group 14 elements, such as silicon (Si), leading to compounds like disiloxanes.
Ethers function as Lewis bases, not Lewis acids, due to the electron-rich nature of the oxygen atom's lone pairs.
Answer: True
The oxygen atom in ethers possesses lone pairs of electrons, enabling it to donate electron density and act as a Lewis base, forming coordinate covalent bonds with Lewis acids. It does not exhibit electron-deficient character characteristic of Lewis acids.
What is the general formula representing ethers in organic chemistry?
Answer: R-O-R'
The fundamental structural motif of ethers involves an oxygen atom bonded to two organyl (alkyl or aryl) groups, yielding the general formula R–O–R′.
What is the approximate bond angle at the oxygen atom in the C-O-C linkage of dimethyl ether, indicating its geometry?
Answer: 111 degrees
The C-O-C bond angle in dimethyl ether is approximately 111 degrees, deviating from the ideal tetrahedral angle due to the repulsion from the two lone pairs on the oxygen atom.
According to valence bond theory, what is the hybridization state of the oxygen atom in ethers?
Answer: sp3
Valence bond theory posits that the oxygen atom in ethers, analogous to its hybridization in water and alcohols, is sp3 hybridized, accommodating two lone pairs of electrons and two sigma bonds to carbon atoms.
Compared to simple hydrocarbons, the alpha hydrogens in ethers are:
Answer: More acidic due to oxygen's higher electronegativity.
The electronegativity of the oxygen atom in ethers polarizes the adjacent C-H bonds, making the alpha hydrogens more susceptible to abstraction (i.e., more acidic) than those found in alkanes.
How do the alpha hydrogens of ethers compare in acidity to those of carbonyl groups (ketones/aldehydes)?
Answer: They are significantly less acidic.
While alpha hydrogens in ethers are more acidic than those in simple hydrocarbons, they are significantly less acidic than the alpha hydrogens adjacent to carbonyl groups (ketones and aldehydes), due to the resonance stabilization of the enolate anion.
Besides carbon, what other elements from Group 14 can form ether linkages?
Answer: Silicon (Si)
While carbon is the most common element forming ether linkages (C-O-C), analogous structures can be formed with other Group 14 elements, such as silicon (Si), leading to compounds like disiloxanes.
Ethers act as Lewis bases because the oxygen atom:
Answer: Possesses lone pairs of electrons that can be donated.
The oxygen atom in ethers possesses lone pairs of electrons, enabling it to donate electron density and act as a Lewis base, forming coordinate covalent bonds with Lewis acids.
Ethers are classified as symmetrical when the two organyl groups attached to the oxygen atom are different.
Answer: False
The classification of ethers as symmetrical or unsymmetrical depends on the identity of the organyl groups bonded to the oxygen. Symmetrical ethers possess two identical groups (R = R'), whereas unsymmetrical ethers have two different groups (R ≠ R').
Diethyl ether is an example of an unsymmetrical ether.
Answer: False
Diethyl ether, with the formula CH3CH2–O–CH2CH3, has two identical ethyl groups attached to the oxygen atom, classifying it as a symmetrical ether.
In the IUPAC nomenclature system, ethers are systematically named using the format 'alkoxyalkane.'
Answer: True
The IUPAC naming convention designates one alkyl group as an 'alkoxy' substituent and the other as the parent alkane. For example, CH3OCH2CH3 is named methoxyethane.
For simple ethers, trivial names are commonly used, which are formed by combining the names of the two organyl substituents followed by the word 'ether.'
Answer: True
Trivial nomenclature for ethers involves listing the names of the alkyl or aryl groups attached to the oxygen atom in alphabetical order, followed by the word 'ether.' For example, ethyl methyl ether.
Esters contain the C-O-C linkage but are classified as ethers.
Answer: False
Esters contain a carbonyl group adjacent to the C-O-C linkage (R-COO-R'), which distinguishes them fundamentally from ethers (R-O-R'). They belong to a separate class of organic compounds.
How are ethers classified if the two organyl groups attached to the oxygen atom are different?
Answer: Mixed or unsymmetrical ethers
Ethers are classified as unsymmetrical (or mixed) when the two organyl groups attached to the oxygen atom are chemically distinct.
Which of the following is a common example of a simple or symmetrical ether?
Answer: Diethyl ether
Diethyl ether, with the formula CH3CH2–O–CH2CH3, is a symmetrical ether as both organyl groups are ethyl groups.
What is the IUPAC naming convention for ethers?
Answer: Alkoxyalkane
The IUPAC naming convention designates one alkyl group as an 'alkoxy' substituent and the other as the parent alkane. For example, CH3OCH2CH3 is named methoxyethane.
Which of the following is the trivial name for CH3OC2H5?
Answer: Ethyl methyl ether
Trivial nomenclature for ethers involves listing the names of the alkyl or aryl groups attached to the oxygen atom in alphabetical order, followed by the word 'ether.' Thus, CH3OC2H5 is ethyl methyl ether.
Which of the following compounds contains a C-O-C linkage but is NOT classified as an ether?
Answer: An ester (e.g., ethyl acetate)
Esters contain a carbonyl group adjacent to the C-O-C linkage (R-COO-R'), which distinguishes them fundamentally from ethers (R-O-R'). They belong to a separate class of organic compounds.
Simple ethers tend to have boiling points that are quite similar to those of alkanes with comparable molecular weights.
Answer: True
Due to their nonpolar nature and lack of hydrogen bonding, ethers exhibit boiling points comparable to alkanes of similar molecular mass, generally lower than isomeric alcohols.
Among the common simple ethers, Tetrahydrofuran (THF) exhibits the highest dipole moment.
Answer: True
Tetrahydrofuran (THF), a cyclic ether, possesses a significant dipole moment (approximately 1.74 D) due to its ring structure and the polarity of the C-O bonds, making it a more polar solvent than acyclic ethers like diethyl ether.
Diethyl ether has a solubility of 69 grams per liter of water at room temperature.
Answer: True
Diethyl ether exhibits moderate solubility in water, approximately 69 grams per liter at standard temperature and pressure, attributed to its ability to form hydrogen bonds with water molecules via the ether oxygen.
Ethers generally exhibit low chemical reactivity due to the strength of their C-O bonds, making them resistant to most bases.
Answer: True
The C-O bonds in ethers are relatively strong and lack readily abstractable protons or electrophilic/nucleophilic centers under typical conditions, rendering them largely inert towards many reagents, particularly bases.
How do the boiling points of simple ethers generally compare to those of alkanes of similar molecular weight?
Answer: Quite similar
Due to their nonpolar nature and lack of hydrogen bonding, ethers exhibit boiling points comparable to alkanes of similar molecular mass, generally lower than isomeric alcohols.
Which ether listed has the highest dipole moment (1.74 D)?
Answer: Tetrahydrofuran (THF)
Tetrahydrofuran (THF), a cyclic ether, possesses a significant dipole moment (approximately 1.74 D) due to its ring structure and the polarity of the C-O bonds, making it a more polar solvent than acyclic ethers like diethyl ether.
What is the approximate solubility of diethyl ether in water at room temperature?
Answer: 69 g/L
Diethyl ether exhibits moderate solubility in water, approximately 69 grams per liter at standard temperature and pressure, attributed to its ability to form hydrogen bonds with water molecules via the ether oxygen.
Ethers are generally considered to have:
Answer: Low chemical reactivity, slightly more than alkanes.
The C-O bonds in ethers are relatively strong and lack readily abstractable protons or electrophilic/nucleophilic centers under typical conditions, rendering them largely inert towards many reagents, particularly bases. They are generally considered less reactive than alkenes but slightly more reactive than alkanes.
What is the primary reason ethers are resistant to most bases?
Answer: The strength of their C-O bonds.
The C-O bonds in ethers are relatively strong and lack readily abstractable protons or electrophilic/nucleophilic centers under typical conditions, rendering them largely inert towards many reagents, particularly bases.
The Williamson ether synthesis involves the reaction of an alkoxide ion with an alkyl halide, not directly with an alcohol.
Answer: True
The Williamson ether synthesis is a nucleophilic substitution reaction where an alkoxide ion (RO-) acts as the nucleophile, attacking an alkyl halide (R'-X) to form an ether (R-O-R'). The alkoxide is typically generated from an alcohol and a strong base.
The Ullmann condensation is a reaction similar to the Williamson synthesis but is used for forming diaryl ethers from aryl halides, typically requiring a copper catalyst.
Answer: True
The Ullmann condensation is a copper-catalyzed reaction specifically utilized for the synthesis of diaryl ethers, typically involving the coupling of aryl halides.
Epoxides are typically prepared by the oxidation of alkenes, not their reduction.
Answer: True
Epoxides, which are cyclic ethers containing a three-membered ring, are commonly synthesized via the oxidation of alkenes, often using peroxyacids. Reduction of alkenes typically yields alkanes.
The direct dehydration of alcohols to form symmetrical ethers requires low temperatures and basic catalysts.
Answer: False
The acid-catalyzed dehydration of alcohols to form symmetrical ethers typically requires elevated temperatures (around 125-150 °C) and strong acid catalysts, not low temperatures and basic catalysts.
Acid-catalyzed dehydration of alcohols to form ethers typically occurs at temperatures around 170°C.
Answer: False
The acid-catalyzed dehydration of alcohols to form ethers typically occurs at temperatures around 125-150 °C. Higher temperatures (around 170 °C) favor alkene formation.
Elimination reactions forming alkenes are the primary competing reaction during the acid-catalyzed dehydration of alcohols intended for ether synthesis.
Answer: True
During the acid-catalyzed dehydration of alcohols, elimination reactions leading to alkene formation are a significant competing pathway alongside ether synthesis, particularly under conditions favoring elimination.
The Williamson ether synthesis is fundamentally characterized as:
Answer: Nucleophilic displacement of an alkyl halide by an alkoxide.
The Williamson ether synthesis is a classic method for preparing ethers, involving the nucleophilic attack of an alkoxide ion on a primary or secondary alkyl halide, resulting in an SN2 displacement.
What is a primary drawback of the Williamson ether synthesis when considering industrial-scale production?
Answer: It produces significant amounts of salt waste.
A significant limitation of the Williamson ether synthesis for large-scale industrial applications is the generation of substantial salt byproducts, which increases waste disposal costs and complicates purification.
The Ullmann condensation is a synthetic route predominantly employed for the preparation of which class of ethers?
Answer: Diaryl ethers
The Ullmann condensation is a copper-catalyzed reaction specifically utilized for the synthesis of diaryl ethers, typically involving the coupling of aryl halides.
What is the most common synthetic pathway for the preparation of epoxides?
Answer: By the oxidation of alkenes.
Epoxides are commonly prepared through the oxidation of alkenes. This transformation can be achieved using various oxidizing agents, such as peroxyacids (e.g., m-CPBA) or via halohydrin intermediates.
During the acid-catalyzed dehydration of alcohols, what competing reaction pathway can lead to alkene formation?
Answer: Elimination reactions forming alkenes
The acid-catalyzed dehydration of alcohols can proceed via two main pathways: ether formation (bimolecular dehydration) and elimination to form alkenes (unimolecular or bimolecular elimination). The latter is a significant competing reaction, particularly at higher temperatures or with secondary/tertiary alcohols.
The direct dehydration of alcohols to form ethers typically requires which conditions?
Answer: High temperature (e.g., 125°C) and an acid catalyst.
The acid-catalyzed dehydration of alcohols to form ethers typically requires elevated temperatures (around 125-150 °C) and strong acid catalysts, not low temperatures and basic catalysts.
Ethers can be cleaved by hydrobromic acid (HBr) and hydroiodic acid (HI).
Answer: True
Ethers can be cleaved by strong protic acids, specifically hydrobromic acid (HBr) and hydroiodic acid (HI), due to their strong acidity and the nucleophilicity of their halide ions.
Upon cleavage of methyl ethers by HBr or HI, the reaction yields an alcohol and a methyl halide.
Answer: True
The cleavage of methyl ethers by HBr or HI yields a methyl halide (e.g., CH3Br from HBr) and the corresponding alcohol (ROH) if the other group is not methyl. For example, R-O-CH3 + HI → ROH + CH3I.
Which acids are capable of cleaving ethers?
Answer: Hydroiodic acid (HI) and Hydrobromic acid (HBr)
Ethers can be cleaved by strong protic acids, specifically hydrobromic acid (HBr) and hydroiodic acid (HI), due to their strong acidity and the nucleophilicity of their halide ions.
What hazardous compounds can form when ethers are stored in the presence of air or oxygen?
Answer: Explosive organic peroxides
When ethers are stored in the presence of air or oxygen, they can undergo autoxidation to form potentially explosive organic peroxides, such as diethyl ether hydroperoxide.
Vinylethers, also known as enol ethers, are a class of ethers that are less common than their alkyl or aryl counterparts and play a role as important intermediates in the field of organic synthesis.
Answer: True
Vinylethers, or enol ethers, represent a specific subclass of ethers characterized by an oxygen atom attached to a vinylic carbon. While less prevalent than simple alkyl ethers, they are synthetically valuable intermediates.
The historical name for diethyl ether was 'spirit of salt.'
Answer: False
The historical name for diethyl ether was 'sweet oil of vitriol,' derived from its early preparation involving sulfuric acid (oil of vitriol).
Polyethers are a type of polymer characterized by the presence of ether linkages within their main molecular chain.
Answer: True
Polyethers are macromolecules where repeating ether linkages (-R-O-) form the backbone of the polymer chain, distinguishing them from polymers with ether linkages solely in pendant groups.
Crown ethers are linear polyethers used primarily as solvents.
Answer: False
Crown ethers are cyclic polyethers, not linear. Their primary function is not as general solvents but as selective complexing agents for metal cations, acting as phase transfer catalysts.
The repeating unit for polyethylene glycol (PEG) is –CH2CH2O–.
Answer: True
Polyethylene glycol (PEG), also known as polyethylene oxide (PEO), is a polymer composed of repeating ethylene oxide units, with the structural formula –CH2CH2O–.
Delrin is a trade name associated with polytetrahydrofuran (PTHF).
Answer: False
Delrin is a trade name for polyoxymethylene (POM), a type of polyacetal. Polytetrahydrofuran (PTHF) has trade names such as Terathane and PolyTHF.
Methyl tert-butyl ether (MTBE) is an example of a commercially important fuel-grade ether produced via alcohol addition to alkenes.
Answer: True
MTBE is synthesized by the acid-catalyzed addition of methanol to isobutylene, a process involving alcohol addition to an alkene, and has been widely used as a gasoline additive.
Ethylene oxide is a cyclic ether and is also classified as the simplest epoxide.
Answer: True
Ethylene oxide is recognized as the simplest epoxide, a three-membered cyclic ether. Its strained ring structure imparts significant reactivity and industrial importance.
Diethyl ether has historically been used as a refrigerant and in the manufacture of smokeless gunpowder.
Answer: True
Diethyl ether has found diverse applications, including use as a solvent, an early anesthetic, a starting fluid for engines, a refrigerant, and historically in the production of smokeless gunpowder and perfumery.
Tetrahydrofuran (THF) is a cyclic ether recognized as one of the most polar simple ethers, making it a highly effective and widely used solvent.
Answer: True
Tetrahydrofuran (THF) is distinguished by its relatively high polarity among simple ethers, rendering it a highly effective and versatile solvent for a broad range of chemical reactions and applications.
Polyethylene glycol (PEG) finds applications in cosmetics and pharmaceuticals, while polypropylene glycol is used in the production of polyurethanes.
Answer: True
Polyethylene glycol (PEG) is extensively utilized in cosmetic and pharmaceutical formulations due to its biocompatibility and solubility. Polypropylene glycol serves as a key component in the synthesis of polyurethanes.
Anisole, also known as methoxybenzene, is an aryl ether recognized for its presence as a principal component in the essential oil derived from anise seed.
Answer: True
Anisole is a characteristic component of the essential oil obtained from anise seeds, contributing to its distinctive aroma and flavor profile.
Crown ethers are cyclic polyethers known for their ability to selectively complex and solubilize metal cations, acting as phase transfer catalysts.
Answer: True
Crown ethers are cyclic polyethers renowned for their ability to selectively complex and solubilize metal cations, acting as effective phase transfer catalysts by transporting these ions into organic phases.
What was the historical name for diethyl ether?
Answer: Sweet oil of vitriol
The historical name for diethyl ether was 'sweet oil of vitriol,' derived from its early preparation involving sulfuric acid (oil of vitriol).
What structural feature defines polyethers?
Answer: Ether linkages within their main molecular chain.
Polyethers are macromolecules where repeating ether linkages (-R-O-) form the backbone of the polymer chain, distinguishing them from polymers with ether linkages solely in pendant groups.
What is the primary function of crown ethers in chemistry?
Answer: As phase transfer catalysts.
Crown ethers are cyclic polyethers renowned for their ability to selectively complex and solubilize metal cations, acting as effective phase transfer catalysts by transporting these ions into organic phases.
The repeating unit for polyethylene glycol (PEG) is given as:
Answer: –CH2CH2O–
Polyethylene glycol (PEG), also known as polyethylene oxide (PEO), is a polymer composed of repeating ethylene oxide units, with the structural formula –CH2CH2O–.
Which trade name is associated with polyoxymethylene (POM)?
Answer: Delrin
Delrin is a trade name for polyoxymethylene (POM), a type of polyacetal. Polytetrahydrofuran (PTHF) has trade names such as Terathane and PolyTHF.
Identify the ether from the following options that is NOT typically classified as a commercially important fuel-grade additive produced by the acid-catalyzed addition of alcohols to alkenes.
Answer: Diethyl ether
While MTBE, TAME, and ETBE are widely used fuel additives derived from alcohol-alkene addition, diethyl ether is primarily known as a solvent and historically as an anesthetic, not a fuel additive in this context.
Ethylene oxide is notable for which characteristic?
Answer: The simplest epoxide.
Ethylene oxide is recognized as the simplest epoxide, a three-membered cyclic ether. Its strained ring structure imparts significant reactivity and industrial importance.
What are the primary applications of polyethylene glycol (PEG) and polypropylene glycol, respectively?
Answer: Cosmetics/Pharmaceuticals and Polyurethanes
Polyethylene glycol (PEG) is extensively utilized in cosmetic and pharmaceutical formulations due to its biocompatibility and solubility. Polypropylene glycol serves as a key component in the synthesis of polyurethanes.
Anisole, also known as methoxybenzene, is an aryl ether recognized for its presence as a principal component in the essential oil derived from which botanical source?
Answer: Anise seed
Anisole is a characteristic component of the essential oil obtained from anise seeds, contributing to its distinctive aroma and flavor profile.
Which of the following accurately describes a characteristic property of crown ethers?
Answer: They selectively bind metal cations.
Crown ethers are cyclic polyethers renowned for their ability to selectively complex and solubilize metal cations, acting as effective phase transfer catalysts by transporting these ions into organic phases.
Identify the option that does NOT represent a historically or currently recognized application of diethyl ether.
Answer: Monomer for polyethylene
Diethyl ether has been utilized as an anesthetic, a solvent, and a starting fluid for diesel engines. Its use as a monomer for polyethylene synthesis is not documented.
Tetrahydrofuran (THF) is primarily recognized for which of the following characteristics?
Answer: One of the most polar simple ethers, a highly effective solvent.
Tetrahydrofuran (THF) is distinguished by its relatively high polarity among simple ethers, rendering it a highly effective and versatile solvent for a broad range of chemical reactions and applications.
What is the nature of the adduct formed when diethyl ether reacts with boron trifluoride (BF3)?
Answer: A coordination complex (borane diethyl etherate)
Diethyl ether, acting as a Lewis base, readily forms a stable coordination complex with the Lewis acid boron trifluoride (BF3), yielding the compound borane diethyl etherate (BF3·O(CH2CH3)2).
Ethers can form stable complexes with strong acids, which effectively prevents the formation of hazardous peroxides.
Answer: False
While ethers can form complexes with Lewis acids, strong protic acids can cleave ethers. Furthermore, complexation with acids does not prevent peroxide formation; in fact, improper storage conditions, such as exposure to air and light, promote it. Peroxides are typically formed via autoxidation.
To prevent peroxide formation, ethers should never be distilled to dryness.
Answer: True
Distilling ethers to dryness is a dangerous practice because peroxides, which are less volatile than the ether, can concentrate in the distillation residue, posing an explosion hazard.
The appearance of a blood-red color upon addition of ferrous sulfate and potassium thiocyanate to an ether sample indicates the presence, not absence, of peroxides.
Answer: True
The formation of a blood-red color in the test involving ferrous sulfate and potassium thiocyanate is a positive qualitative test for the presence of organic peroxides in ether samples.
Storing ethers in the presence of aldehydes is a recommended precaution to prevent peroxide formation.
Answer: True
The presence of aldehydes or other radical scavengers can inhibit the autoxidation process that leads to peroxide formation in ethers. Therefore, storing ethers with such additives is a recommended safety practice.
What is the standard chemical test for detecting the presence of peroxides in aged ether samples?
Answer: Shaking with ferrous sulfate and potassium thiocyanate, looking for a blood-red color.
The presence of peroxides in ether samples is typically detected using a qualitative test involving ferrous sulfate and potassium thiocyanate. A blood-red color indicates a positive result for peroxides.