Are ethers capable of hydrogen bonding

In water, the charge is localized only on the hydrogens and not delocalized spread throughout as with the alkyl groups, so the charge is stronger in water than in ethers. Like water, ether is capable of forming hydrogen bonds. However, because of the delocalized nature of the positive charge on the ether molecule's hydrogen atoms, the hydrogens cannot partake in hydrogen bonding.

Thus, ethers only form hydrogen bonds to other molecules that have hydrogen atoms with strong partial positive charges. Therefore, ether molecules cannot form hydrogen bonds with other ether molecules. This leads to the high volatility of ethers. Ethers are capable, however, of forming hydrogen bonds to water, which accounts for the good solubility of low molecular weight ethers in water.

Table shows boiling points for some simple ethers and the boiling points of alcohols of the same number of carbon atoms. Notice that due to the hydrogen bonding between alcohol molecules, all alcohols have appreciably higher boiling points than their isomeric ethers. In fact, with the exception of the alkanes, cycloalkanes and fluorocarbons, ethers are probably the least reactive common class of organic compounds.

The inert nature of the ethers relative to the alcohols is undoubtedly due to the absence of the reactive O—H bond. A general anesthetic acts on the brain to produce unconsciousness and a general insensitivity to feeling or pain. Figure 9. This painting shows an operation in Boston in in which diethyl ether was used as an anesthetic. Inhalation of ether vapor produces unconsciousness by depressing the activity of the central nervous system. Diethyl ether is relatively safe because there is a fairly wide gap between the dose that produces an effective level of anesthesia and the lethal dose.

However, because it is highly flammable and has the added disadvantage of causing nausea, it has been replaced by newer inhalant anesthetics, including the fluorine-containing compounds halothane, and the halogenated ethers, desflurane, isoflurane, and sevoflurane. The halogenated ethers, isoflurane, desflurane, and sevoflurane, show reduced side effects when compared with diethyl ether.

Unfortunately, the safety of these compounds for operating room personnel has been questioned. For example, female operating room workers exposed to halothane suffer a higher rate of miscarriages than women in the general population. Ethers are also common functional groups found in natural products and can have unique biological activities.

In fact, some very large compounds containing multiple ethers, called polyethers, have been found to cause neurotoxic shellfish poisoning. In this example, the dinoflaggelate, Karina brevis, which is the causative agent of red tide algal blooms, produces a class of highly toxic polyethers called the brevatoxins. Brevatoxin A is depicted in Figure 9. Symptoms of this poisoning include vomiting and nausea and a variety of neurological symptoms such as slurred speech.

The dinoflaggelate, Karina brevis, shown in the upper left is the causative agent of red tide harmful algal blooms. These marine algal blooms can be quite extensive as shown in the photo of a red tide upper right occurring near San Diego, CA. Brevatoxin A is depicted as an example. Filter feeding clams and muscles become contaminated with the dinoflaggelate and can cause neurotoxic shellfish poisoning if eaten. Red tides can have severe economic costs as fisheries and shellfish harvesting has to be closed until toxin levels in commercial products return to acceptable levels.

Aldehydes are typically more reactive than ketones. These structures can be found in many aromatic compounds contributing to smell and taste. As discussed before, we understand that oxygen has two lone pairs of electrons hanging around. These electrons make the oxygen more electronegative than carbon. The polarizability is denoted by a lowercase delta and a positive or negative superscript depending on the atom.

Properties of Aldehydes and Ketones Aldehydes In aldehydes, the carbonyl group has a hydrogen atom attached to it together with either a second hydrogen atom or, more commonly, a hydrocarbon group which might be an alkyl group or one containing a benzene ring. For the purposes of this section, we shall ignore those containing benzene rings. Below are some examples of aldehydes Notice that these all have exactly the same end to the molecule. All that differs is the complexity of the other carbon group attached.

When you are writing formulae for these, the aldehyde group the carbonyl group with the hydrogen atom attached is always written as -CHO — never as COH. That could easily be confused with an alcohol. Ketones In ketones, the carbonyl group has two carbon groups attached. Again, these can be either alkyl groups or ones containing benzene rings.

Notice that ketones never have a hydrogen atom attached to the carbonyl group. That means that ethanal boils at close to room temperature. Larger aldehydes and the ketones are liquids, with boiling points rising as the molecules get bigger. The size of the boiling point is governed by the strengths of the intermolecular forces.

There are two main intermolecular forces found in these molecules: London dispersion forces: These attractions get stronger as the molecules get longer and have more electrons. That increases the sizes of the temporary dipoles that are set up. This is why the boiling points increase as the number of carbon atoms in the chains increases — irrespective of whether you are talking about aldehydes or ketones.

Dipole-Dipole attractions: Both aldehydes and ketones are polar molecules because of the presence of the carbon-oxygen double bond. As well as the dispersion forces, there will also be attractions between the permanent dipoles on nearby molecules. That means that the boiling points will be higher than those of similarly sized hydrocarbons — which only have dispersion forces. It is interesting to compare three similarly sized molecules. They have similar lengths, and similar although not identical numbers of electrons.

The polarization of carbonyl groups also effects the boiling point of aldehydes and ketones which is higher than those of hydrocarbons of similar size. However, since they cannot form hydrogen bonds, their boiling points tend to be lower than alcohols of similar size.

Table 9. Note that compounds that have stronger intermolecular forces have higher boiling points. The solubility of aldehydes and ketones are therefore about the same as that of alcohols and ethers. As the carbon chain increases in length, solubility in water decreases. The borderline of solubility occurs at about four carbon atoms per oxygen atom.

All aldehydes and ketones are soluble in organic solvents and, in general, are less dense than water. Back to the Top Aldehydes and Ketones in Nature Similar to the other oxygen-containing functional groups discussed thus far, aldehydes and ketones are also widespread in nature and are often combined with other functional groups.

Examples of naturally occurring molecules which contain a aldehyde or ketone functional group are shown in the following two figures. The compounds in the figure 9. Many of these molecular structures are chiral and have distinct stereochemistry. When chiral compounds are found in nature they are usually enantiomerically pure, although different sources may yield different enantiomers. For example, carvone is found as its levorotatory R -enantiomer in spearmint oil, whereas, caraway seeds contain the dextrorotatory S -enantiomer.

In this case the change of the stereochemistry causes a drastic change in the perceived scent. Aldehydes and ketones are known for their sweet and sometimes pungent odors. The odor from vanilla extract comes from the molecule vanillin. Likewise, benzaldehyde provides a strong scent of almonds. Because of their pleasant fragrances aldehyde and ketone containing molecules are often found in perfumes. However, not all of the fragrances are pleasing.

In particular, 2-Heptanone provides part of the sharp scent from blue cheese and R -Muscone is part of the musky smell from the Himalayan musk deer. Lastly, ketones show up in many important hormones such as progesterone a female sex hormone and testosterone a male sex hormone.

Notice how subtle differences in structure can cause drastic changes in biological activity. The ketone functionality also shows up in the anti-inflammatory steroid, Cortisone. Acetone is also produced as a breakdown product of acetoacetic acid.

Acetone can then be excreted from the body through the urine or as a volatile product through the lungs. Normally, ketones are not released into the bloodstream in appreciable amounts. Instead, ketones that are produced during lipid metabolism inside cells are usually fully oxidized and broken down to carbon dioxide and water.

This is because glucose is the primary energy source for the body, especially for the brain. Glucose is released in controlled amounts into the bloodstream by the liver, where it travels throughout the body to provide energy.

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Molecules that are capable of engaging in hydrogen bonding can be hydrogen bond acceptors HBA , hydrogen bond donors HBD , or both. As I am sure you know, a molecule is said to be capable of forming hydrogen bonds if it has a hydrogen atom bonded to one of the three most electronegative elements in the periodic table : N, O, or F.

I'll use the "H-O" bond as an example. What such a bond implies is that a significant partial positive charge will develop on the hydrogen atom and a significant partial negative charge will appear on the more electronegative atom, creating a permanent dipole moment. Now, in order for a hydrogen bond to form between two molecules, the partial positive hydrogen must interact with an electronegative atom that has lone pairs and a dipole moment.

Take water, for example. One partial positive hydrogen on a water molecule will be attracted to one lone pair present on the partial negative oxygen of another water molecule. Hydroperoxides exist as hydrogen-bonded dimers in nonpolar solvents and readily form hydrogen-bonded associations with ethers, alcohols, amines, ketones, sulfoxides, and carboxyhc acids Other physical properties of hydroperoxides have been reported The unshared electron pairs of the ether oxygens , which give the polymer strong hydrogen bonding affinity, can also take part in association reactions with a variety of monomeric and polymeric electron acceptors 40, These include poly acryhc acid , poly methacryhc acid , copolymers of maleic and acryflc acids, tannic acid , naphthoHc and phenoHc compounds, as well as urea and thiourea 42— Effective cosolvents are less polar and have cycHc stmctures.

They include aUphatic and aromatic hydrocarbons , ethers, sulfides, and ketones. Acidic or hydrogen-bonding solvents have an opposite effect , rendering the polar aprotic component less effective.