Comprehensive breakdown of ketones and aldehydes., Cheat Sheet of Chemistry

Download Comprehensive breakdown of ketones and aldehydes. and more Cheat Sheet Chemistry in PDF only on Docsity! Module - 34.1 Carbonyl Compounds Introduction: Oxygen compounds in which oxygen is bonded to a carbon atom through a double bond are known as carbonyl compounds. The functional unit (> C=O), present in these compounds is called carbonyl group. The carbon atom of this group has two remaining bonds that may be occupied by hydrogen or alkyl or aryl groups. If at least one of these groups is hydrogen, the compound is an aldehyde. If both the groups are hydrocarbon groups the compound is a ketone. 2 R-C Aldehyde: R = alkyl group *y H Ri c=0 Ketone : R! and R2 = alkyl or aryl groups R2 Aldehydes and ketones are simple but most important carbonyl compounds. Nomenclature: The naming of carboxyl compounds i.e. aldehydes and ketones, is done in two ways. They are a. Common method or trivial method and b. IUPAC method a. Common (naming) method: This is used for a few compounds only. The names of the aldehydes are derived from the names of the corresponding carboxylic acid. The part “— oic acid or “— ic acid” in the name of the acid is replaced by “— aldehyde”. Ex: Form (ic acid) + Formaldehyde Benz (oic acid) — benzaldehyde The carbon atoms in the chain are indicated either by the Greek alphabets a, 8, r .... or by numerical indecies. 1, 2,3..... The examples given below indicate the method of identifying the carbons in the chain. By Greek alphabets By numerical prefixes Starts from the carbon next to Numbering starts from the aldehydic carbonyl carbon. carbon in aldehydes. IUPAC nomenclature of ketones: Examples: 3-—methyl cyclopentanone 2,4—-Dimethyl pentan—3-one O a, «! - Dimethyl Pentan—3-one 1 0 5 2 L, I, Il; l, | 5. —C=¢=-C=-C=C— 41 rit ti CH; CH; CH; Structure of the Carbonyl Group: The aldehydes and ketones have at least one carbonyl group as the functional group. The carbonyl carbon is sp? hybridized. It has three sp? hybrid orbitals and one unhybridized p-orbital. It uses sp? hybrid orbitals to form three o — bonds. One with oxygen atom and the remaining two with two other atoms or groups (R’s or Ar’s or H’r). All these three sigma bonds lie in the same plane and are at an angle of 120°. The fourth valence electron, which remains in the unhybridized p-orbital overlaps with the p-orbital of oxygen to form a TT — bond. The oxygen atom has two lone pairs of electrons, which occupy the remaining orbitals on oxygen atom. The carbonyl! carbon and the three atoms bonded to it lie in the same plane and the pi-electron cloud is above and below this plane. Rec ° Since the carbon and the oxygen atoms have different values of electronegativity, the bond between carbon and oxygen is a polar bond. The electron density around the oxygen atom is greater. This causes the development of partial positive charge (6+) on carbon and a partial negative charge (5-) on oxygen atoms. NEF ST c=0 Polar bond Thus the carbonyl carbon is an electrophilic centre (Lewis acid) while the carbonyl oxygen is a nucleophilic (Lewis base) centre. These carbonyl compounds have significant dipole moments. The dipole moment of carbonyl compounds is due to the highly polar character of the carbonyl group. This, in turn, can be explained on the basis of resonance involving a neutral structure. (Structure |) and a dipolar structure (Structure II) ° ° li =— bk G c os ax Structure! Structure Il Neutral structure Dipolar structure The common (trivial) and IUPAC names of some aldehydes and ketones are given in below Table Aldehyde Trivial Name | IUPAC Name C2HsCHO propionaldehyde Propanal CHy=—— CH= CHO. lsobutyraldehyde 2 — Methylpropanal CH, B a CHs:——= CH= CHCHO, tds butyraldehye B-bromo-a-—methyl 3-Bromo-2- methibutanal cH,— CH, — Ba —éu—cno _B- Chloro — a — ethyl 3—Chloro — 2 — ethyl | ee cl CH;—CH, valeraldehyde pentanal Ketone | Trivial IUPAC CH3COCH2CH2CH3 Methyl, n — propyl "Pentan — 2-one/2 — ketone pentanone (CHs)2CHCOCH(CHs)2_ Diisopropyl ketone a- o Cf Methylcyclohexanone CH 3 (CHs)2C = CHCOCH; __ Mesityl oxide 2, 4-—Dimethylpentan — 3 — one 2 - Methylcyclohexanone 4—Methylpent -3-en-2-_ one COD Pron Act Srtortctens: Aldehydes are prepared from acid chlorides by reaction with He in the Presence of palladium catalyst Supported on barium sulphate. The catalyst is poisoned by acicition of sulphur or quinoline, The poisoning IS GONG tO @VOld Ine TUrther reduction Of alcdenydes to alcohols. This FEACtON Is Called ROSeNMUNEds reaction, > aT “y 2 me Oe et n— Bice. . ———— CH. COC! « H. —sareasST Acetyl entorica Cannot be obtained by Rosenmuncd's reaction. Ketones are obtained by reacting acical Chlorices with cialky! cacrmmiurny, 2RCOCI+ Car, ——— 2RCOR’ + Calc, Ketone Structure of carboxyl compounds: Carbonyl compounds from hydrocarbons | q T | From alkanes by By hydration of alkynes in the From nitriles From acid chlorides ozonolysis presence of HgSO, with dil H,SO, {Rosen mund’s reaction] (i) H2C + CH, + O03 (i) HC =CH + H,0 (i) With acidified SnCl, at (i) Aldehydes with H2 in canoe H,SO,+HgSO, room temperature. the presence of . oY; Boil with H20 to give Pd—BaSO, 5 ‘ Wz aldehydes R.COCI Hs Hic’, CHS H3C-C H,C.C = N + 2[H] + HCI oe iva Nu Ether 290K oe oo daneH,o ————— HC.CH = NH. HCl RCL H,0/6 4 [H.C = 0 +O = CH} My H3C.CHO + NH,CI (i) HAC (ii) Any other alkyne (ii) wits Grlenard seneent. (ii) Ketones with CdR}, C= CH, + O03 HC= CH + H,0 Srolysis with tg R.CO.CI + CdR, H3C sat [onrinnasenns R.C = N + R'Mgex ‘ ; R R.CO = O + CdCl. . Pa J ; Hite H3C-CO- CH; Nee NiMex i ch CH, R nc7 | ae RE pro oO oO RL a 2n+H,O c=0 HC R C=0+0=CH, Pa 2 4. Aromatic aldehydes from aromatic hydrocarbons: (a) By oxidation of methylbenzenes: Oxidation of an aromatic compound having a methyl group on the benzene ring with CrOzin the presence of acetic anhydride followed by hydrolysis gives the corresponding benzaldehyde. CH(OCOCH;), cHO CH; a. eS 2NaOH Cy 1cH,c0,0 Cy he, +2CH,COONa + 2H,0 Benzylidene diacetate Further oxidation of the benzaldehyde to benzoic acid is prevented as the aldehyde forms a non-oxidisable benzylidene diacetate derivative. This reaction is called the Etard reaction. (b) By side chain chlorination followed by hydrolysis: Side chain chlorination of toluene gives benzal chloride, which on hydrolysis gives benzaldehyde. This is a commercial method of manufacture of benzaldehyde. CH CHCl, Cl,/hv 4.0 — > 373K Toluene Benzal Chloride Benzaldehyde CHO (c) By Gattermann —- Koch reaction: When benzene or its derivative is treated with carbon monoxide and hydrogen chloride in the presence of anhydrous aluminium chloride or cuprous chloride, it gives benzaldehyde or substituted benzaldehyde. CHO CO, HCI —_—— Anhyd. AICI,, 90 atm Benzene Benzaldehyde Physical Properties: (a) (b) Physical state: Lower aldehydes are either gases or low boiling liquids.Other aldehyde and ketones are liquids or solids at room temperature. Lower aldehydes have sharp pungent odors. As the size of the molecule increases, the odor becomes less pungent and more fragrant. Lower ketones are colorless liquids and have pleasant smell. The higher members are colorless solids. Aromatic ketones are usually solids with a pleasant smell. Boiling points: Aldehydes and Ketones have relatively high boiling point as compared to hydrocarbons of comparable molecular masses. This is because the aldehydes and ketones contain polar carbonyl group and therefore have stronger intermolecular dipole - dipole interactions between the opposite ends of C=O dipoles. However, their boiling points are lower than those of alcohols of comparable molecular masses because unlike alcohols, they cannot form intermolecular hydrogen bonds. Name of the b.pt.(K) Molar Mass compound n—- Butane 273 58 Propanal 322 58 Acetone 329 58 Propan — | - ol 370 60