Chapter 2 Introduction to organic compounds Nomenclature Physical properties Conformation Organic compounds Ch 2 #2 in Organic Chemistry 1 hydrocarbons [RH] alkanes alkenes alkynes alkyl halides [RX] ethers [ROR’] alcohols [ROH] amines [RNH2] in Org Chem 2 aromatic comp’ds carbonyl comp’ds Alkanes Ch 2 #3 saturated hydrocarbons saturated ~ all single bonds; no multiple bond [= or ≡] hydrocarbon [HC] ~ contains only C and H <cf> carbohydrate homologs general formula ~ CnH2n+2 differs by CH2 (methylene) paraffins non-polar, hydrophobic Ch 2 #4 Constitutional isomers Ch 2 #5 isomers [異性質體] same composition, different structure (and shape) constitutional isomer = structural isomer = skeletal isomer two or more compounds with the same molecular formula [composition] different structural formula [connectivity] e.g. C H O 2 6 H H H H H C C O H H C O C H H H H H eg C4H10 Constitutional isomers in alkanes Ch 2 #6 straight-chain vs branched alkanes ‘iso’ ~ C bonded to 1 H and 2 methyls [CH3] neopentane Ch 2 #7 # of possible isomers as # of atoms C20H42 has 366,319 isomers! drawn? calculated? nomenclature ~ naming common name = trivial name systematic name = IUPAC name Alkyl substituents [groups] Ch 2 #8 R ~ alkyl R with =, alkenyl; R with ≡, alkynyl RH is alkane, and If R covers alkyl, alkenyl, and alkynyl, RH is HC. Isomeric alkyls Ch 2 #9 propyl n ~ normal, commonly omitted (n-)propyl ~ CH3CH2CH2- isopropyl ~ (CH3)2CH- butyl CH3 sec- (or s-) tert- or t- Degree of substitution of carbon CH3 H3C CH3 H3C CH C C C CH3 primary [1°] H H carbon 2 2 secondary [2°] tertiary [3°] quaternary [4°] carbon carbon carbon Ch 2 #10 primary hydrogen? pentyl pentyl isopentyl tert-pentyl IUPAC name perferred sec-? sec-? neopentyl Ch 2 #11 commonly used alkyl groups OH isobutyl alcohol NH2 sec-butylamine (Systematic) nomenclature of alkanesCh 2 #12 1. Determine the number of carbons in the longest continuous chain. longest continuous chain = parent HC = root chain ‘root+ane’ Ch 2 #13 2. Number the chain so that the substituent gets the lowest number. #-[substituent][parent] iso, sec-, tert- are common names; but accepted to IUPAC system when no # in common name used as part of substituent Ch 2 #14 3. Number the substituents to yield the lowest possible number. Substituents are listed in alphabetical order. If two or more same subs, use di, tri, tetra, penta, --- . ‘di, tri, ---’ and ‘sec-, tert-’ are ignored in alphabetizing . ‘iso’ and ‘cyclo’ are not ignored Ch 2 #15 4. Assign the lowest possible numbers to all of the substituents 5. If the same numbers in both directions, the first group cited receives the lower number Ch 2 #16 6. If two or more longest chains of the same length, the parent is the chain with the greatest number of subs. Ch 2 #17 7. For branched substituent, 5-(2-methylpropan-1-yl)decane may use common name; iso, sec-, tert- much simpler systematic 1. Find the longest chain beginning at the branch. 2. Number from the branching point. 3. Put (#-name) in parentheses. * ‘di, tri, ---’ are not ignored in alphabetizing. Skeletal structure Ch 2 #18 skeletal structure = bond-line structure draw by line(-bond) structure drawing a line for a (C-C) bond = Kekule structure not showing C and H bonded to C H H H H H H CH3 H H C H C H H3C CH3 H C C C C C C H H3C CH C C C CH3 H2 H2 H H H H C H H H H O H H O H H C O H C O H CH3 C C H H OH OH C C H H OCH3 H H Cycloalkanes Ch 2 #19 cycloalkane ~ cyclic alkane ~ alkane in a ring, CnH2n acyclic ~ open-chain Nomenclature 1. (subs)cycloalkane If subs has more C than ring, cycloalkylalkane 2. Name two subs’ in alphabetical order; Give 1- to the first. Ch 2 #20 3. If more than 2 subs’: i) List alphabetically, ii) Give 1- to the subs letting the second subs the lowest #, iii) So on. 4-ethyl-1,2-dimethylcyclohexane Alkyl halides Ch 2 #21 RX types nomenclature alkyl halide (common) or haloalkane (IUPAC) Ethers Ch 2 #22 ROR (symmetrical) or ROR’ (unsymmetrical) nomenclature common name ~ alkyl alkyl ether ( ) . Common name is common [preferred] for simple ethers. IUPAC name ~ alkoxyalkane Alcohols Ch 2 #23 ROH ~ with hydroxy [OH] group types nomenclature common name ~ alkyl alcohol IUPAC name ~ alkanol ‘ol’ for hydroxy ‘functional group’ Functional group Ch 2 #24 center of reactivity in molecules site where reaction takes place priority of functional groups alkoxyalkane haloalkane Ch 2 #25 IUPAC nomenclature for comp’d with functional group # just before ‘ol’ or before name Find the longest chain containing functional group [FG] Give lowest # to C with FG diol, triol, --- Ch 2 #26 For FG and subs, FG gets lowest #. priority of FG If # the same for FG, then lowest # for subs If more than 2 subs, alphabetical order Amines Ch 2 #27 RNH2, RR’NH, RR’R”N types ~ depends on # of alkyls not on DS of C nomenclature common name ~ alkylamine, alkylalkylamine, -- (one word) Ch 2 #28 IUPAC name ~ alkanamine rules the same as for alcohols . lowest # for amine; then for subs; subs alphabetical N- for 2° and 3° amines Ch 2 #29 NH2 triethylamine N OH N,N-diethylethanamine 5-aminohexan-2-ol quaternary ammonium salt Structure of RX, ROR’, ROH, and RNHCh2 2 #30 all sp3 C, O, and N Intermolecular interactions [forces] Ch 2 #31 (1) instantaneous dipole-induced dipole interaction betw non-polar molecules (London) dispersion force weak (2) dipole-dipole interaction betw polar molecules [permanent dipoles] stronger than (1) van der Waals force usually, (1) + (2) ~ 0.5 – 5 kcal/mol in a narrow sense, (1) only Ch 2 #32 (3) hydrogen bonding dipole-dipole interaction δ+ betw H on EN atom [N, O, F] and δ– EN atom [N, O, F] fairly strong (3 – 8 kcal/mol) due to high ∆EN and H(2.1) C(2.5) short distance (small H) N(3.0) O(3.5) F(4.0) Cl(3.0) H on C? H on Cl? strength the same? O-H is a better H-bond donor larger ∆EN -N: is a better accepter more loose e pair Physical properties of RY Ch 2 #33 boiling point liquid to gas ~ separation ~ depends on intermol force bp with size [molecular weight] larger contact area RH ~ low bp (1) only ROR’ ~ bp higher than RH (2) ROH ~ much higher bp (3) amines lower bp than ROH relative H-bond strength bp ~ 1° > 2° > 3° RX bp ~ RF < RCl < RBr < RI larger µ larger polarizability larger X Ch 2 #34 melting point solid to liquid ~ mobility ~ also dep on intermol forces trend the same to bp except for the effect of molecular shape symmetric, compact close packing high mp mp bp even-odd effect p95 Ch 2 #35 solubility dissolution = mixing solvent [1] and solute [2] ∆Gmix = ∆Hmix – T ∆Smix ∆Smix > 0 always . As Temp up, T∆S up ∆Hmix depends on 1-2 interaction . intermolecular interaction betw 1 and 2 ‘like dissolves like’ {polar, hydrophilic, water-soluble} vs {nonpolar, hydrophobic, oil-soluble [organic]} RH ~ nonpolar ~ water-insoluble . floats on water ~ density of C30 < 1 Ch 2 #36 ROH ~ water-solubility depends on size and shape of R . propanol soluble with water; butanol not . butyl alcohol less soluble than t-butyl alcohol OH OH ROR’ ~ less water-soluble than ROH . Ether is a good choice of solvent for organic reactions. not very reactive [stable], not very polar [dissolves organics] Lewis base [dissolves salts (cations)], not protonic [useful for base] amine ~ 1° > 2° > 3° more water-soluble RX ~ R-F more water-soluble polarity and H-bonding Conformation and configuration Ch 2 #37 conformation spatial arrangements formed by rotation around single bond 2 conformers ~ 1 compound ~ not separable configuration spatial arrangements formed with breaking (double) bond 2 isomers ~ 2 comp’ds ~ different properties ~ separable Conformations of ethane Ch 2 #38 Rotation around C-C bond gives 2 conformations. staggered conformer eclipsed conformer conformer = conformational isomer? = rotational isomer? = configurational isomer? ~ NOT isomer, but one compound Staggered conformer is of lower energy. due to hyperconjugation? C-H σ and C-H σ* due to (the absence of) repulsion between C-H bonding electrons ~ torsional strain ~ 1 kcal/mol x 3 Ch 2 #39 Newman projection and potential energy map Actually, numerous conformations. 3 max’s (eclipsed) and 3 min’s (staggered) front carbon (C1) rear carbon (C2) rotate C2 60° dihedral angle [二面角] Ch 2 #40 RT RT K ∆G = – RT ln K K = exp [– ∆G/RT] K = exp [– 2.9/(.002)(300)] = .008 at 300 K Prob(eclipsed) = .008/1.008 = .8% at 300 K Most of ethane molecule is in staggered conformation. = Ethane is in staggered conformation most of times. Conformations of butane Ch 2 #41 3 max (syn, eclipsed) and 3 min (anti, gauche) (syn) gauche eclipsed anti eclipsed gauche Ch 2 #42 anti of the lowest energy (most stable) gauche H3C CH3 higher energy than anti due to steric strain ~ repulsion between (non-bonded) groups ~ 0.87 eclipsed torsional + steric strain 1 x 3 + 0.4 x 2 = 3.8 Ch 2 #43 (syn) of the highest energy torsional + steric strain 1 x 3 + 1.5 = 4.5 higher alkanes all-anti planar zigzag ~ most stable, but not most probable Conformations of cycloalkanes Ch 2 #44 6- (and 5-)membered rings are most popular. Cyclic comp’ds are strained. (angle+torsional+steric strain) strain ~ 6, 12 or larger < 5, 7-11 < 4 < 3 equivalent to Table 2.9 p104 Ch 2 #45 cyclopropane (has to be) planar high angle strain high torsional strain (planar) most highly strained cyclobutane if planar, 90° bond angle and fully eclipsed by puckering, angle strain , torsional strain slightly nonplanar [puckered] ~ butterfly still,