Carboxylic acids are derivatives of hydrocarbons containing one or more carboxyl groups.
The number of carboxyl groups characterizes the basicity of the acid.
Depending on the number of carboxyl groups, carboxylic acids are divided into monobasic carboxylic acids (containing one carboxyl group), dibasic (containing two carboxyl groups) and polybasic acids.
Depending on the type of radical associated with the carboxyl group, carboxylic acids are divided into saturated, unsaturated and aromatic. Limiting and unsaturated acids are combined under the general name of aliphatic or fatty acids.
Monobasic carboxylic acids
1.1 Homologous series and nomenclature
The homologous series of monobasic saturated carboxylic acids (sometimes called fatty acids) begins with formic acid
Homologous series formula
The IUPAC nomenclature permits the preservation of many acids by their trivial names, which usually indicate the natural source from which this or that acid was isolated, for example, formic, acetic, butyric, valeric, etc.
For more complex cases, the names of acids are derived from the name of hydrocarbons with the same number of carbon atoms as in the acid molecule, with the addition of the ending -ovaya and words acid. Formic acid H-COOH is called methanoic acid, acetic acid CH 3 -COOH is called ethanoic acid, etc.
Thus, acids are considered as derivatives of hydrocarbons, one link of which is converted into carboxyl:
When naming branched chain acids according to rational nomenclature, they are considered as derivatives of acetic acid, in the molecule of which hydrogen atoms are replaced by radicals, for example, trimethylacetic acid (CH 3) 3 C - COOH.
1.2 Physical properties of carboxylic acids
Only from purely formal positions can the carboxyl group be considered as a combination of carbonyl and hydroxyl functions. In fact, their mutual influence on each other is such that it completely changes their properties.
The polarization of the C=0 double bond, common for carbonyl, increases strongly due to the additional contraction of a free electron pair from the neighboring oxygen atom of the hydroxyl group:
This results in a significant reduction O-N connections in hydroxyl and the ease of splitting off a hydrogen atom from it in the form of a proton (H +). The appearance of a reduced electron density (δ+) on the central carbon atom of the carboxyl also leads to contraction of the σ-electrons of the neighboring C-C connections to the carboxyl group and the appearance (as in aldehydes and ketones) of a reduced electron density (δ +) on the α-carbon atom of the acid.
All carboxylic acids are acidic (detected by indicators) and form salts with hydroxides, oxides and carbonates of metals and with active metals:
Carboxylic acids in most cases are dissociated in aqueous solution only to a small extent and are weak acids, significantly inferior to such acids as hydrochloric, nitric and sulfuric. So, when dissolving one mole in 16 liters of water, the degree of dissociation of formic acid is 0.06, acetic acid - 0.0167, while hydrochloric acid is almost completely dissociated with this dilution.
For most monobasic carboxylic acids RK but \u003d 4.8, only formic acid has a lower pKa value (about 3.7), which is explained by the absence of the electron-donating effect of alkyl groups.
In anhydrous mineral acids, carboxylic acids are protonated at oxygen to form carbocations:
The shift of electron density in the molecule of undissociated carboxylic acid, which was mentioned above, lowers the electron density on the hydroxyl oxygen atom and increases it on the carbonyl one. This shift is further increased in the anion of the acid:
The result of the shift is a complete equalization of the charges in the anion, which actually exists in the form A - the resonance of the carboxylate anion.
The first four representatives of the carboxylic acid series are mobile liquids, miscible with water in all respects. Acids, the molecule of which contains from five to nine carbon atoms (as well as isobutyric acid), are oily liquids, their solubility in water is low.
Higher acids (from C 10) are solids, practically insoluble in water; during distillation under normal conditions, they decompose.
Formic, acetic and propionic acids have a pungent odor; the middle members of the series have an unpleasant odor, the higher acids have no odor.
The physical properties of carboxylic acids are affected by a significant degree of association due to the formation of hydrogen bonds. Acids form strong hydrogen bonds, since the O-H bonds in them are highly polarized. In addition, carboxylic acids are able to form hydrogen bonds with the participation of the oxygen atom of the carbonyl dipole, which has a significant electronegativity. Indeed, in the solid and liquid state, carboxylic acids exist mainly in the form of cyclic dimers:
Such dimeric structures persist to some extent even in the gaseous state and in dilute solutions in non-polar solvents.
The carboxyl group combines two functional groups - carbonyl and hydroxyl, mutually influencing each other. This influence is transmitted through the conjugation system sp 2 -atoms O–C–O.
Electronic structure The –COOH group gives carboxylic acids their characteristic chemical and physical properties.
1. The shift of the electron density to the carbonyl oxygen atom causes an additional (compared to alcohols and phenols) polarization of the О–Н bond, which determines the mobility of the hydrogen atom ( acid properties).
In an aqueous solution, carboxylic acids dissociate into ions:
However, carboxylic acids in general are weak acids: in aqueous solutions, their salts are highly hydrolyzed.
Video experience "Carboxylic acids - weak electrolytes".
2. Reduced electron density (δ+) on the carbon atom in the carboxyl group makes it possible for reactions nucleophilic substitution-OH groups.
3. The -COOH group, due to the positive charge on the carbon atom, reduces the electron density on the hydrocarbon radical associated with it, i.e. is in relation to him electron-withdrawing deputy. In the case of saturated acids, the carboxyl group exhibits -I -the effect, and in unsaturated (for example, CH 2 \u003d CH-COOH) and aromatic (C 6 H 5 -COOH) - -I And -M -effects.
4. The carboxyl group, being an electron acceptor, causes additional polarization of the C–H bond in the neighboring (α-) position and increases the mobility of the α-hydrogen atom in substitution reactions at the hydrocarbon radical.
See also "Reaction centers in carboxylic acid molecules".
Hydrogen and oxygen atoms in the -COOH carboxyl group are capable of forming intermolecular hydrogen bonds, which largely determines physical properties carboxylic acids.
Due to the association of molecules, carboxylic acids have high boiling and melting points. Under normal conditions, they exist in a liquid or solid state.
For example, the simplest representative, formic acid HCOOH, is a colorless liquid with bp. 101 ° C, and pure anhydrous acetic acid CH 3 COOH, when cooled to 16.8 ° C, turns into transparent crystals resembling ice (hence its name glacial acid).
Video experience "Ice acetic acid".
The simplest aromatic acid - benzoic C 6 H 5 COOH (mp. 122.4 ° C) - easily sublimes, i.e. changes to the gaseous state without going through the liquid state. When cooled, its vapors sublimate into crystals. This property is used to purify a substance from impurities.
Video experience "Sublimation of benzoic acid".
The solubility of carboxylic acids in water is due to the formation of intermolecular hydrogen bonds with the solvent:
The lower homologues C 1 -C 3 are miscible with water in any ratio. As the hydrocarbon radical increases, the solubility of acids in water decreases. Higher acids such as palmitic C 15 H 31 COOH and stearic C 17 H 35 COOH are colorless solids that are insoluble in water.
The elements included in the carboxyl group have an unequal electronegativity value: C (sp 2) - 2.69; O - 3.5 and H - 2.2. The electron density is shifted towards oxygen, which leads to bond polarization. The carboxyl group is a planar conjugated system in which p,p-conjugation occurs when the p-orbital of the oxygen atom of the hydroxo group interacts with the p-bond. The presence of p,p-conjugation in the carboxyl group of carboxylic acids contributes to the uniform distribution of the negative charge in the carboxylate ion formed upon the elimination of a proton.
The presence of p,p-conjugation in the carboxyl group of carboxylic acids significantly increases the acidic properties of carboxylic acids compared to alcohols. The oxygen of the OH group experiences a certain deficit of electrons, so it causes a shift in the electron density from the hydrogen atom to itself. The hydrogen atom becomes mobile and can leave in the form of a proton. Proton mobility promotes the formation of salts of carboxylic acids (reaction mechanism S E).
For carboxylic acids, the reactions of nucleophilic substitution of the OH group in the carboxyl (SN mechanism) are most characteristic. In reactions in which an atom (or a group of atoms) is replaced by a nucleophile, nucleophilic substitution S N takes place. Nucleophiles are electron donors: OH - , RO - , CN - , -NH 2 , R-O-R, R-OH, etc. In S N reactions, an atom (or groups of atoms) with a negative charge is split off from the molecule and replaced by a nucleophile:
The more stable the leaving ion (:X), the easier the nucleophilic substitution reactions proceed. The S N reactions of carboxylic acids proceed in the presence of an acid catalyst. The reactions of nucleophilic substitution of hydroxyl at the sp 2 -hybridized carbon atom lead to the formation of functional derivatives of carboxylic acids:
1. esterification reaction. The substitution of the hydroxyl in the carboxyl with the rest of the alcohol leads to the formation of esters. The esterification reaction occurs when acids are heated with alcohols in the presence of water-removing substances:
CH 3 COOH + C 2 H 5 OH ↔ CH 3 CO-OS 2 H 5 + H 2 O
ethyl acetate
The reaction is reversible and proceeds until equilibrium is established. The shift of equilibrium to the right is carried out due to the removal of one of the final products from the reaction mixture.
The hydrolysis of esters (unlike the esterification reaction) can be carried out in both acidic and alkaline conditions.
2. Acid halides are derivatives in which the hydroxyl group of the carboxyl is replaced by a halogen. Acid halides are formed by the action of phosphorus halides (PCl 5, PCl 3) or thionyl chloride (SOCl 2) on acid:
Acid halides are highly active nucleophiles; they are used in various syntheses as active acylating agents for introducing an acid residue into the substance molecule.
3. Formation of acid anhydrides- substitution of a hydroxyl in a carboxyl for an acid residue.
Anhydrides of monocarboxylic acids are most often obtained by the interaction of acid chlorides and sodium salts of these acids.
4. Formation of acid amides- substitution of hydroxyl in carboxyl for an ammonia residue - an amino group - NH 2
The reaction proceeds better if ammonia acts on acid halides.
5. In the human body, formation reactions are quite common. thioethers. So, tissues contain thiol HS-KoA (coenzyme A - acylation coenzyme), which can react with carboxylic acids according to the equation:
CH 3 COOH + HS-KoA → H 2 O + CH 3 CO-S-CoA
Reactions of this kind are catalyzed by complex enzyme systems and end with the formation of thioethers, in this form carboxylic acids are used in metabolic reactions.
Decarboxylation is one of the most important reactions of carboxylic acids. Unsubstituted monocarboxylic acids are difficult to decarboxylate.
Dibasic carboxylic acids are easily decarboxylated when heated:
HOOS-COOH → HCOOH + CO 2
HOOS - CH 2 -COOH → CH 3 COOH + CO 2
Of great importance is the enzymatic decarboxylation of α- and β-oxo acids, as well as α-amino acids in the body.
In aqueous solutions, carboxylic acids dissociate:
CH 3 COOH ↔ CH 3 COO - + H +
All carboxylic acids are weak electrolytes (HCOOH - medium strength). Carboxylic acids in electrophilic substitution reactions form salts:
CH 3 COOH + NaOH → CH 3 COOHa + H 2 O
Oxalic acid salts (oxalates) are sparingly soluble and often form kidney and bladder stones (oxalate stones). These salts include calcium oxalate.
4. Illustrative material: presentation
5. Literature:
Main literature:
2. Seitembetov T.S. Chemistry: textbook - Almaty: TOO "EVERO", 2010. - 284 p.
3. Bolysbekova S. M. Chemistry of biogenic elements: tutorial- Semey, 2012. - 219 p. : silt
4. Verentsova L.G. Inorganic, physical and colloidal chemistry: textbook - Almaty: Evero, 2009. - 214 p. : ill.
5. Physical and colloidal chemistry / Under the editorship of A.P. Belyaev .- M .: GEOTAR MEDIA, 2008
6. Verentseva L.G. Inorganic, physical and colloidal chemistry, (verification tests) 2009
Additional literature:
Test "Pyaterochka"
(Some questions may have more than one answer.)
1. Which of the following acids are organic?
A) Ant; b) nitrogen;
B) sulfuric; d) lemon.
2. Why are ant stings painful?
A) Fired with formic acid;
B) secrete poison;
C) corrode with formic alkali;
D) stick sharp teeth.
3. What are salts of carboxylic acids called?
A) acetates; b) bustilates;
B) propylates; d) postulates.
4. What name of acid does not exist?
A) lemon b) oxalic;
B) wine d) grape.
5. What acids are vitamins?
A) nicotine; b) ascorbic;
B) acetylsalicylic; d) amber.
Lecture #5
1. Subject: Carbohydrates.
2. Purpose: To form knowledge about the classification, about the structure, about the chemical properties of carbohydrates. The study of the topic contributes, forms knowledge about the structure and properties of carbohydrates, as a basis for understanding their metabolism in a living organism
3. Abstracts of the lecture:
3.1. Lecture plan
1. Carbohydrates, classification, Fisher carbonyl and projection formulas, Colley-Tollens formulas, Haworth formulas.
2. Monosaccharides - structure, isomerism, tautomerism.
3. Chemical properties of monosaccharides
4. Disaccharides: maltose, cellobiose, lactose, sucrose.
5. Polysaccharides: homopolysaccharides and heteropolysaccharides.
6. The biological significance of carbohydrates.
3.2. Abstracts of the lecture
Carbohydrates are organic compounds widely distributed in nature. The term "carbohydrates" was proposed in 1844 by the chemist K. Schmidt (Russia) due to the fact that most representatives of this class corresponded in composition to a combination of carbon and water, for example: C 6 H 12 O 6 → 6C + 6H 2 O; C n (H 2 O) n.
The class of carbohydrates is divided into two groups:
- simple carbohydrates (monosaccharides) or monoses
- complex carbohydrates (homopolysaccharides and heteropolysaccharides)
Simple carbohydrates cannot be hydrolyzed, while complex carbohydrates are hydrolyzed to form simple carbohydrates.
Monosaccharides are heterofunctional compounds. They are aldehydes and ketones of polyhydric alcohols (or their cyclic hemiacetals). Depending on the presence of an aldehyde or ketone group, aldoses and ketoses are distinguished. Monosaccharides contain from 3 to 10 carbon atoms in a molecule.
The isomerism of monosaccharides is associated with the presence of: 1) aldehyde and ketone groups; 2) asymmetric carbon atoms (optical isomerism). The belonging of monosaccharides to the D- or L-series is determined by the rule of M.A. Rozanov: according to the configuration of the asymmetric carbon atom farthest from the senior (carbonyl) group (pentose C-4, hexose C-5).
Carbonyl formulas of hexoses:
D-glucose D-mannose D-galactose D-fructose
Monosaccharides exist as acyclic (carbonyl forms) and cyclic hemiacetal forms. Acyclic and cyclic forms of monosaccharides are isomers with respect to each other. This kind of isomerism is called cyclo-oxo-tautomerism.
Cyclic (Haworth) hexose formulas:
a-D-glucose b-D-glucose a-D-galactose b-D-fructose
For sugars in cyclic form, it is possible conformational isomerism, associated with the arrangement in space of the carbon atoms of the six-membered cycle. Reactions of hemiacetal hydroxyl. Monosaccharides having the structure of cyclic hemiacetals, when interacting with alcohols in the presence of an acid catalyst under anhydrous conditions, form complete acetals.
a-D-galactopyranose Methyl-a-D-galactopyranoside
Hemiacetal or glycosidic hydroxyl does not exhibit the properties of alcohols, but behaves specifically, forming O- and N-glycosides. Glycosides, like all acetals, are hydrolyzed in an acidic environment and are resistant to dilute alkalis. The hydrolysis of glycosides is the reverse reaction of the formation of glycosides
As polyhydric alcohols, monosaccharides dissolve copper (II) hydroxide, forming a blue chelate. This reaction is used to detect monosaccharides and glycosides.
Ethers formed by interaction with haloalkanes. Simultaneously with the alcohol hydroxyl groups, the hemiacetal hydroxyl also reacts, resulting in a glycoside ether.
Ether Esters: α-glucose and α-fructose phosphates
Esters are formed by the reaction of esterification of OH groups under the action of oxygen-containing acids (organic and inorganic) or their anhydrides. Esters of phosphoric acid - phosphates are of biological importance.
Recovery carbonyl group of monosaccharides with hydrogen on nickel or palladium leads to the formation of polyhydric alcohols: glucose - sorbitol (D-glucite), mannose - mannitol, D-xylose - xylitol, galactose - dulcite. Xylitol and sorbitol are sweet-tasting crystalline substances that are highly soluble in water and are used as sugar substitutes for diabetes. Sorbitol is an intermediate product in the industrial production of ascorbic acid (vitamin C).
Oxidation of monosaccharides.
Scheme chemical reaction C x (H 2 O) y + xO 2 ® xCO 2 + uH 2 O + Q corresponds to the process of complete oxidation (combustion) of carbohydrates.
Depending on the conditions of oxidation of monosaccharides, glycan, glycar and glycuronic acids are formed.
Neutral environment. Only the aldehyde group is oxidized to the carboxyl group in a neutral or acidic medium (mild oxidation). Oxidation of glucose with bromine water in the presence of chalk (goes to neutralize the resulting HBr) at room temperature leads to the formation of gluconic (glyconic) acid:
gluconic acid glucaric acid glucuronic acid
Gluconic acid in the form of calcium salts (calcium glucanate) has found wide application in practical medicine (for allergies, increased permeability of blood vessels, etc.).
acid environment. When monosaccharides are heated with dilute nitric acid, the primary alcohol group at the other end of the monosaccharide chain is oxidized simultaneously with the aldehyde group, which leads to the formation of dibasic hydroxy acids (glycaric acids). Glucose is glucaric acid.
Alkaline environment. When oxidized in an alkaline environment with heating, monosaccharides undergo profound changes with the splitting of the carbon chain. In this case, oxidizing agents such as silver oxide Ag 2 O (silver mirror reaction) and copper (II) hydroxide Сu (OH) 2 are reduced to metallic silver and copper oxide (I) (Trommer test).
In the tissues of the human body, during the oxidation of glucose, glucuronic acid can be formed (the aldehyde group is protected and preserved, only the primary alcohol group is oxidized). When galactose is oxidized, galacturonic acid is formed. Uronic acids play a protective role in the human liver, participating in the neutralization of toxic substances that come from outside or are formed as a result of vital activity. Decarboxylation of uronic acids leads to the formation of pentoses (glucuronic acid → xylose + CO 2).
Derivatives of monosaccharides
Deoxysugars called derivatives of monosaccharides in which one or two HO groups are replaced by a hydrogen atom, for example, 2-deoxyribose.
Amino Sugar- are formed on the basis of monosaccharides, in the molecules of which the OH group of the second link is replaced by an amino group - NH 2, for example, β,D-glucosamine.
Neuraminic acid . Obtained as a result of aldol condensation of PVC (1) and D-mannosamine (2):
sialic acids. They are N-acetyl derivatives of neuraminic acid. Acylation occurs with an acetyl or hydroxyacetyl residue.
Complex carbohydrates- These are compounds, during the hydrolysis of which monosaccharides and their derivatives are formed. Depending on the structure and number of structural components, complex carbohydrates are usually divided into oligosaccharides(2-10 monoses) and polysaccharides.
disaccharides formed from two monosaccharides. Their general empirical formula is C 12 H 22 O 11. The most important disaccharides are maltose, lactose, sucrose, and cellobiose. Maltose(malt sugar) - a reducing disaccharide - consists of residues of 2 D-glucopyranose molecules linked by an alpha-1,4-glycosidic bond; during hydrolysis, it is cleaved into two D-glucoses (D-glucopyranoses).
Lactose(milk sugar) is a reducing disaccharide. Found in the milk of mammals. Upon hydrolysis, it forms 2 monosaccharides: β-D-galactopyranose (β-D-galactose) and D-glucose.
sucrose(cane sugar, beet sugar) is the most famous and widespread sugar. During hydrolysis, sucrose is split into α-glucose and β-fructose. The α-1, β-2-glycosidic bond is formed by the hemiacetal hydroxyls of α-glucose and β-fructose, so there is no possibility for cyclo-oxotautomerism. Sucrose is a non-reducing disaccharide.
Cellobiose- a reducing disaccharide, consists of residues of 2 molecules of β-D-glucopyranose linked by a beta-1,4-glycosidic bond. It is obtained by hydrolysis of cellulose (fiber).
Polysaccharides- these are high-molecular carbohydrates, chemically related to polyglycosides, i.e. are products of polycondensation of monosaccharides linked by glycosidic bonds.
Polysaccharide chains can be branched (amylopectin, glycogen) and unbranched, that is, linear (fiber, amylose).
According to their composition, polysaccharides are divided into
1. homopolysaccharides- biopolymers formed from residues of one monosaccharide;
2. heteropolysaccharides- biopolymers formed from residues of different monosaccharides.
All of them have a common name: glycans.
Starch- is a reserve polysaccharide of most plants, in which it is formed due to the reaction of photosynthesis. Starch is not homogeneous in structure - it is a mixture of two polysaccharides: amylose and amylopectin in a ratio of 10-20% to 80-90%. amylose consists of a-D-glucopyranose residues linked by a(1®4)-glycosidic bonds. An amylose macromolecule can include from 200 to 1000 monomer residues. Amylopectin is a homopolysaccharide of a branched structure, in which the linear chain of a-D-glucopyranose residues is built due to a (1®4) glycosidic bonds, and the branching elements are formed due to a (1®6) glycosidic bonds. Between the branch points fit from 20 to 25 glucose residues; the molecular weight of amylopectin is 1-6 million units.
4. Illustrative material: presentation
5. Literature:
Main literature:
1. Bioorganic chemistry: textbook. Tyukavkina N.A., Baukov Yu.I. 2014
- Seitembetov T.S. Chemistry: textbook - Almaty: TOO "EVERO", 2010. - 284 p.
- Bolysbekova S. M. Chemistry of biogenic elements: textbook - Semey, 2012. - 219 p. : silt
- Verentsova L.G. Inorganic, physical and colloidal chemistry: textbook - Almaty: Evero, 2009. - 214 p. : ill.
- Physical and colloidal chemistry / Under the editorship of A.P. Belyaev .- M .: GEOTAR MEDIA, 2008
- Verentseva L.G. Inorganic, physical and colloidal chemistry, (verification tests) 2009
Additional literature:
- Ravich-Shcherbo M.I., Novikov V.V. Physical and colloidal chemistry. M. 2003.
2. Slesarev V.I. Chemistry. Fundamentals of the chemistry of the living. St. Petersburg: Himizdat, 2001
3. Ershov Yu.A. General chemistry. Biophysical chemistry. Chemistry of biogenic elements. M.: VSh, 2003.
4. Asanbayeva R.D., Iliyasova M.I. Theoretical basis structure and reactivity of biologically important organic compounds. Almaty, 2003.
- Guide to laboratory studies in bioorganic chemistry, ed. ON THE. Tyukavkina. M., Bustard, 2003.
- Glinka N.L. General chemistry. M., 2003.
- Ponomarev V.D. Analytical chemistry part 1,2 2003
6. test questions(Feedback):
- How many % of the daily diet in a balanced diet should be carbohydrates?
- What causes a lack of carbohydrates in food?
- What causes an excess of carbohydrates in food?
Lecture #6
1. Subject:α-amino acids. Peptides. Squirrels.
2. Purpose: to study the structure, properties, ways of formation, α-amino acids in the body. The study of the topic contributes, forms the knowledge of the composition, structure and biological role of α-amino acids, peptides and proteins, to study the biological functions of proteins on molecular level
3. Abstracts of the lecture:
3.1. Lecture plan
1. The structure of amino acids, classification. isomerism
2. Ways of formation of amino acids in a living organism.
3. Physical, Chemical properties amino acids.
4. The concept of peptides, their biological significance
5. The structure of the peptide bond
6. Proteins, classification, levels of organization, biological role
7. Hemoglobin is a representative of chromoproteins
8. Qualitative reactions for α-amino acids and proteins
Abstracts of the lecture
Amino acids (AMA) are derivatives of carboxylic acids in the radical of which one or more hydrogen atoms are replaced by amino groups.
The general formula of AMK:
Or an alpha amino acid
There can be several NH 2 and -COOH in amino acid molecules.
According to the position of the amino group in the carbon chain relative to the carboxyl group, α-, β-, γ-amino acids are distinguished. α-amino acids (α-AMA) are protein monomers.
Classification of alpha-amino acids.
1. According to the number of amino and carboxyl groups, there are: monoaminomonocarboxylic acids (glycine, alanine, valine, leucine, isoleucine, serine, threonine, cysteine, methionine, phenylalanine, tyrosine, histidine, tryptophan); monoamino dicarboxylic acids (glutamic acid, aspartic acid, cystine); diaminomonocarboxylic acids (lysine, arginine).
2. By the presence of functional groups in the radical: hydroxyamino acids (serine, threonine); sulfur-containing amino acids (methionine, cysteine, cystine).
3. By the nature of the radical: aliphatic amino acids (glycine, alanine, leucine, etc.); aromatic amino acids (phenylalanine, tyrosine); heterocyclic aromatic amino acids (tryptophan, histidine); heterocyclic imino acids (proline, hydroxyproline).
Amino acid isomerism is associated with the position of functional groups and with the structure of the carbon skeleton. All alpha-amino acids that make up proteins (except GLI) are optically active substances, because contain an asymmetric carbon atom and exist as enantiomers - D– and L- optical isomers. Animal proteins contain L-AMA.
The carboxyl group combines two functional groups - carbonyl and hydroxyl, mutually influencing each other:
The acidic properties of carboxylic acids are due to the shift of the electron density to carbonyl oxygen and the resulting additional (compared to alcohols) polarization of the О–Н bond.
In an aqueous solution, carboxylic acids dissociate into ions:
Derivatives of carboxylic acids: salts, esters, acid chlorides, anhydrides, amides, nitriles, their preparation.
Carboxylic acids are highly reactive. They react with various substances and form a variety of compounds, among which great importance have functional derivatives, i.e. compounds obtained as a result of reactions at the carboxyl group.
1. Formation of salts
a) when interacting with metals:
2RCOOH + Mg ® (RCOO) 2 Mg + H 2
b) in reactions with metal hydroxides:
2RCOOH + NaOH ® RCOONa + H 2 O
2. Formation of esters R"–COOR":
The reaction of formation of an ester from an acid and an alcohol is called an esterification reaction (from lat. ether- ether).
3. Formation of amides:
Instead of carboxylic acids, their acid halides are more often used:
Amides are also formed by the interaction of carboxylic acids (their halides or anhydrides) with organic derivatives of ammonia (amines):
Amides play an important role in nature. Molecules of natural peptides and proteins are built from a-amino acids with the participation of amide groups - peptide bonds
Nitriles - organic compounds general formula R-C≡N are considered as derivatives of carboxylic acids (amide dehydration products) and are referred to as derivatives of the corresponding carboxylic acids, for example, CH 3 C≡N - acetonitrile (acetic acid nitrile), C 6 H 5 CN - benzonitrile (benzoic acid nitrile).
Anhydrides of carboxylic acids can be considered as a condensation product of two -COOH groups:
R 1 -COOH + HOOC-R 2 \u003d R 1 - (CO) O (OC) - R 2 + H 2 O
carboxyl group (carboxyl) -COOH - a functional monovalent group that is part of carboxylic acids and determines their acidic properties.
The structure of the carboxyl group
The carboxyl group combines two functional groups - carbonyl (>C=O) and hydroxyl (-OH), mutually influencing each other.
The acidic properties of carboxylic acids are due to the shift of the electron density to carbonyl oxygen and the resulting additional (compared to alcohols) polarization of the O-H bond.
In an aqueous solution, carboxylic acids dissociate into ions:
R-COOH = R-COO − + H+
Solubility in water and high boiling points of acids are due to the formation of intermolecular hydrogen bonds.
As the molecular weight increases, the solubility of acids in water decreases.
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An excerpt characterizing the Carboxyl group
- Svetodar, Sever... What happened to him? How did the son of Radomir and Magdalena live his life on Earth?..The North thought... Finally, taking a deep breath, as if throwing off the obsession of the past, he began his next exciting story...
- After the crucifixion and death of Radomir, Svetodar was taken to Spain by the Knights of the Temple to save him from the bloody paws of the "holy" church, which, no matter what it cost, tried to find and destroy him, since the boy was the most dangerous living witness, and also , a direct successor of the Radomir Tree of Life, which was supposed to change our world someday.
Svetodar lived and learned about his surroundings in the family of a Spanish nobleman, who was a faithful follower of the teachings of Radomir and Magdalene. They did not have their own children, to their great sadness, so the “new family” received the boy very cordially, trying to create for him the most comfortable and warm home environment. They called him Amory there (which meant dear, beloved), since it was dangerous to call Svyatodar with his real name. It sounded too unusual for someone else's hearing, and risking Svetodar's life because of this was more than unreasonable. So Svetodar for everyone else became an Amory boy, and only his friends and his family called him by his real name. And then, only when there were no strangers nearby ...