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Organic Chemistry III

Chapter 10. Organic Chemistry III. Aldehydes.

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Organic Chemistry III

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  1. Chapter 10 Organic Chemistry III

  2. Aldehydes • An aldehyde is an organic compound containing a terminal carbonyl group. This functional group, which consists of a carbon atom bonded to a hydrogen atom and double-bonded to an oxygen atom (-HC=O), is called the aldehyde (or formyl) group. Nomenclature • For acyclic aliphatic aldehydes: drop the ol on the alcohol name and add al. For example, HCHO, methanal; CH3CH2CH2CHO, butanal. • In other cases, such as when a -CHO group is attached to a ring, the suffix -carbaldehyde may be used, e.g. C6H11CHO, cyclohexanecarbaldehyde. • If replacing the aldehyde group with a carboxyl group (-COOH) would yield a carboxylic acid with a trivial name, the aldehyde may be named by replacing the suffix -ic acid or -oic acid in this trivial name by -aldehyde. HCHO (methanal), formaldehyde HCOOH formic acid CH3CHO (ethanal), acetaldehyde  CH3COOH acetic acid C6H5CHO (phenylmethanal), benzaldehyde C6H5COOH benzoic acid

  3. Ketones • Aketone is a type of compound that features a carbonyl group (C=O) bonded to two other carbon atoms, i.e. R3C-CO-CR3 where R can be a variety of atoms and groups of atoms. • With C=O bonded to two carbon atoms, ketones are distinct from many other functional groups, such as carboxylic acids, aldehydes, esters, amides and other O-containing compounds. The double-bond of the carbonyl group distinguishes ketones from alcohols and ethers. Nomenclature • Drop the ol on the alcohol and add one. When necessary, number the l.c.c. to locate the -C=O group. propanone (acetone) diphenylmethanone (diphenyl ketone, benzophenone) 3 - pentanone

  4. keto-enol tautomerism Use of Aldehydes and Ketones • Aldehyde is easy to be oxidized and undergo keto-enol tautomerism. • Aldehyde is a common building block for the synthesis of more complex compounds and materials and also used as disinfectants and preservatives. • Ketones are difficult to oxidize. • Ketones are produced on massive scales in industry as solvents, polymer precursors, and pharmaceuticals. In terms of scale, the most important ketones are acetone, methylethyl ketone, and cyclohexanone. • Ketones are also common in biochemistry, but less so than in organic chemistry in general. The combustion of hydrocarbons is an uncontrolled oxidation process that give ketones as well as many other types of compounds

  5. Carboxylic Acids • Carboxylic acids are organic acids characterized by the presence of a carboxyl group (-COOH). • Carboxylic acids are Brønsted-Lowry acids – they are proton donors. Salts and anions of carboxylic acids are called carboxylates. • Nomenclature: drop the ol on the alcohol and add oic acid. The mono- and dicarboxylic acids have trivial names. methanoic acid ethanoic acid Butanoic acid

  6. malonic acid (propanedioic acid) maleic acid (cis-butenedioic acid) fumaric acid (trans-butenedioic acid) lactic acid (2-hydroxy propanoic acid) L-valine tricarballylic acid (propane-1,2,3-tricarboxylic acid) Important Acids Fatty acidsare carboxylic acids with long unbranched saturated or unsaturated aliphatic tail (chain) Amino acids have both amine and carboxylic groups - zwitterions

  7. ethyl acetate O CH3COOH + HOCH2CH3 CH3 CO CH2CH3 + H2O Esters • Esters are organic compounds derived by reacting an oxoacid (one containing an oxo group) with a hydroxyl compound such as an alcohol. • Nomenclature: a) Name alcohol part (R') first, then the acid part (R-COO-); b) Name the alcohol part as a radical; c) In naming the acid part, drop the ic ending of the acid and add ate. • Esters generally have pleasant odors. The odors of fruits is due to esters.

  8. aniline 4-methyl-2-aminopentane Amines • Amines are organic compounds and functional groups that contain a basic N atom with a lone pair. Amines are derivatives of NH3, wherein one or more H atoms have been replaced by a substituent of an alkyl or aryl group. Primary Amine Secondary Amine Tertiary Amine Nomenclature • The compound is given the prefix ‘amino-’ or the suffix ‘-amine’. • An organic compound with multiple amino groups is called a diamine, triamine, tetraamine and so forth CH3NH2 methyl amine(aminomethane) H2N(CH2)2NH2 ethylene diamine

  9. Important Properties of Amines • H-bonding significantly influences the properties of primary and secondary amines. Boiling point of amines is higher than those of the corresponding phosphines (PR1R2R3) but generally lower than those of the alcohols. For example, methylamine (CH3NH2) and ethylamine (CH3CH2NH2) are gases under standard conditions, whereas methanol and ethanol are liquids. • Gaseous amines possess a characteristic ammonia smell and liquid amines have a distinctive ‘fishy’ smell. • Most aliphatic amines display some solubility in H2O. Solubility decreases with the increase in the number of carbon atoms. Aliphatic amines display significant solubility in organic solvents, especially polar organic solvents. • The aromatic amines, such as aniline, have their lone pair e’s conjugated into the benzene ring, thus their tendency to engage in hydrogen bonding is diminished. Their boiling points are high and their solubility in water low. • Amines of the type NHRR' and NRR'R" are chiral: the N atom bears four substituents counting the lone pair. The energy barrier for the inversion of the stereocenter is relatively low.

  10. chiral achiral = ≠ Chirality • Chirality is used to describe an object that is non-superposable on its mirror image. Achiral objects are those that are identical to the mirror image. The energy barrier for the inversion of stereocenter is low, which means that the two stereoisomers are rapidly interconverted at RT. As a result, NHRR' cannot be resolved optically and NRR'R" can only be resolved when the R, R', and R" groups are constrained in cyclic structures.

  11. O CH3COOH + HN(CH3)2 CH3 CN (CH3)2 + H2O DMF Amides • Amide usually refers to organic compounds that contain the functional group consisting of an acyl group (R-C=O) linked to a nitrogen atom. N,N-dimethylacetamide • The lone pair of electrons on the nitrogen is delocalized onto the carbonyl, thus forming a partial double bond between N the carbonyl C. Consequently the N in amides is not pyramidal. It is estimated that acetamide is described by resonance structure A for 62% and by B for 28% • The solubilities of amides and esters are roughly comparable. Tertiary amides, with the important exception of N,N-dimethylformamide, exhibit low solubility in water.

  12. Important Functional Groups and Their Reactions

  13. Functional Groups Summary – Hydrocarbons ethane ethylene acetylene 2-phenylpropane 1-bromotoluene

  14. Summary of Groups Containing Halogens chloroethane fluoro methane chloro methane bromo methane iodo methane

  15. Summary of Groups Containing Oxygen_1 acetyl chloride methanol methyl ethyl ketone acetaldehyde sodium acetate

  16. Summary of Groups Containing Oxygen_2 acetic acid diethyl ether ethyl butyrate methyl ethyl ketone peroxide Di-t-butyl peroxide

  17. Summary of Groups Containing Nitrogen acetamide trimethyl amine choline nicotine

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