Basicity of Alcohols
The basicity of alcohols refers to their ability to donate a pair of electrons to a proton. Alcohols are considered weak bases due to the presence of the hydroxyl group, which can accept a proton to form an oxonium ion. The basicity of alcohols can be influenced by factors such as the nature of the alcohol and the solvent environment.
4 Key excerpts on "Basicity of Alcohols"
eBook - ePub- Juan Moreno, Rafael Peinado(Authors)
- 2012(Publication Date)
- Academic Press(Publisher)
...The higher the K a, the stronger the acid and the lower the pK a, since pK a = −logK a. The acidity of these materials is due to the capacity of the carboxylate ion to distribute its excess negative charge between the two oxygens. In general terms, the more stable the ion produced after donation of a proton, the greater the acidic character of the substance in question. Something similar occurs with aromatic alcohols or phenols, which are more acidic than alcohols because the electron can be delocalized around the aromatic ring. An important reaction of acids is the formation of esters with alcohols: Esterification has an equilibrium constant of approximately 4 for most ethyl esters. 3.3 Factors that Influence Acidity Aliphatic Carboxylic Acids The substituents located on the aliphatic chain linked to the carboxyl group have an effect on the stability of the carboxylate ion according to whether they are electron donors or acceptors: a. Substituents that are electron acceptors attract excess electrons from the carboxylate ion and spread the negative charge more effectively. Consequently, they enhance the stability of the ion and increase acidity. b. Substituents that are electron donors (alkyl groups) donate electrons to the carboxylate anion and increase the charge density on the ion...
eBook - ePub- J Fisher, J.R.P. Arnold, Julie Fisher, John Arnold(Authors)
- 2020(Publication Date)
- Taylor & Francis(Publisher)
...Section J - Organic Compounds By Chemical Class J1 Alcohols and related compounds DOI: 10.1201/9780203079522-38 Key Notes Alcohol reactions Alcohols may undergo a wide range of reactions. The presence of an oxygen atom with its two lone pairs of electrons means that alcohols may act as nucleophiles. However, among the most important reactions are those that lead to the loss of water (dehydration reactions), and those that lead to the formation of carbonyl compounds (oxidation reactions). Important alcohols The simplest alcohol, methanol, is commercially produced in huge quantities. Ethanol is the alcohol referred to when talking about alcoholic beverages. In addition to this, it is used therapeutically as a competitive inhibitor to treat ethylene glycol (a diol) poisoning. More complicated alcohols have antiseptic (propan-2-ol) and other therapeutic properties. Aromatic alcohols Benzene-based alcohols are referred to as phenols. Phenol itself is a well known antiseptic, although today phenol derivatives are more commonly used for this purpose. Phenols are weak acids as the anion formed on deprotonati on of the hydroxyl group is stabilized by resonance. Dehydration and oxidation reactions are generally not possible. Ethers Aliphatic ethers are of limited use as reagents in chemical or biochemical processes. However, they are routinely used as solvents for chemical reactions and as anesthetics. Cyclic derivatives of these compounds such as furans and pyrans (and their saturated derivatives) occur in many carbohydrates. Thiols Thiols are the sulfur derivatives of alcohols, and display a number of similar properties. Thiols are most noted for their strong and often unpleasant odors. They are readily oxidized to disulfides, and this is particularly important in protein chemistry...
eBook - ePub- Leon Golberg(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
...In biological systems the relative reactivity of EO with alcoholic OH groups as opposed to aliphatic amine groups of macromolecules is at least an order of magnitude lower. In fact, in the chemical preparation of hydroxyethyl ethers based on aliphatic alcohols, it is necessary to convert the alcoholic OH group to an alkoxide anion, RO”, by way of a strong base to achieve any significant reactivity at all. Similarly, mercaptan groups react with EO to form hydroxyethyl thioethers; mer-capto (sulfhydryl) groups, as in cysteine, are relatively more reactive than aliphatic hydroxyl groups, but significantly less reactive than the much stronger nucleophilic amine groups. Table 3 Rate Constants for the Hydrolysis of EO Temperature °C Acidic L/mol/min Neutral min Basic L/mol/min 20 0.32 0.000022 0.0034 30 1.00 0.000055 0.01 40 2.5 0.00019 0.0306 131 0.173 Other active hydrogen groups, such as found in carboxamide (RCONH 2) groups, or carboxylic acid (RCOOH) groups are essentially unreactive under normal biological systems, although resourceful chemists have found ways to effect hydroxyethylation of such groups by the use of special systems of high pressure, extreme temperatures, catalysts, conversion of reactive groups to other species, etc. Chemically, the conversion of EO to ethylene glycol may be accomplished under acidic or basic conditions; in either case the reaction is far more rapid than under conditions of neutral pH, as indicated in Table 3. Similar reactivity is observed in the reaction of EO with hydrogen acids, such as hydrochloric acid, hydrobromic, etc. An assessment of the magnitude or relative rates of these two reactions must be made in determining the biological implications of testing results of EO, whether such tests are undertaken in animal systems or in vitro systems...
eBook - ePubBiochemistry Explained
A Practical Guide to Learning Biochemistry
- Thomas Millar(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
...Carboxylic or organic acids contain this functional group. Draw the general structure of an alcohol and ethanol. Answer: Nomenclature : The -OH is called an hydroxyl group – learn this. Q&A 1 : For practice, which of the following are alcohols? A B C D Q&A 2 : Indicate which of the following are acids? A B C D E F G H To form an ester bond, we simply condense (form water) the acid with the alcohol. In the following diagram, carboxylic acid is condensed with alcohol to form an ester bond and water: MAJOR POINT 6 : An ester is formed by condensing an acid with an alcohol. Biochemical examples of ester bonds Clearly from above, biochemicals that contain ester bonds must have basic structural elements of alcohols and acids. Examine the following molecule, glycerol. It comprises 3 carbons with an hydroxyl group at each carbon i.e. a poly-alcohol. Although this molecule rarely occurs biochemically, it is one of the most important structures to learn for biochemistry because it is the structural basis for many other biochemicals. It is exciting because it has the potential to form 3 ester bonds, not just one. To form an ester bond, it needs an acid (or 2 or 3 acids). Q&A 3 : Draw a carboxylic acid with 14 carbons (including the carbon of the carboxyl group) and a single bond between each carbon so that it is saturated with hydrogens. Remember that each carbon can only form 4 bonds. When such a long uncharged chain forms would you expect it to he more water or more lipid soluble? Answer: Lipid soluble, because there is very little charge on such a molecule. Therefore a good name for such an acid would be a fatty acid. Q&A 4 : Draw a fatty acid with 20 carbons with double bonds between C5 and C6, C8 and C9, C11 and C12 and between C14 and C1 5 with carbon 1 being the carbon of the carboxylic acid. This fatty acid is not saturated. It has double bonds so could theoretically take more H atoms to saturate the molecule fully...
