Chapter 2 Introduction to organic compounds Nomenclature Physical properties Conformation
Organic compounds Ch 2 #2 in Organic Chemistry 1 hydrocarbons [R] alkanes alkenes alkynes alkyl halides [RX] ethers [ROR ] alcohols [RO] amines [RN 2 ] 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 [C] ~ contains only C and <cf> carbohydrate homologs general formula ~ C n 2n+2 differs by C 2 (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 2 6 O eg C 4 10 C C O C O C
Constitutional isomers in alkanes Ch 2 #6 straight-chain vs branched alkanes iso ~ C bonded to 1 and 2 methyls [C 3 ] neopentane
Ch 2 #7 # of possible isomers as # of atoms C 20 42 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 R is alkane, and If R covers alkyl, alkenyl, and alkynyl, R is C.
Isomeric alkyls Ch 2 #9 propyl (n-)propyl ~ C 3 C 2 C 2 - n ~ normal, commonly omitted isopropyl ~ (C 3 ) 2 C- butyl C 3 Degree of substitution of carbon sec- (or s-) tert- or t- C 3 3 C C3 3 C C C primary [1 ] carbon C 2 secondary [2 ] carbon C 2 tertiary [3 ] carbon C 3 quaternary [4 ] carbon
Ch 2 #10 primary hydrogen? pentyl pentyl isopentyl tert-pentyl IUPAC name perferred sec-? sec-? neopentyl
Ch 2 #11 commonly used alkyl groups O isobutyl alcohol N 2 sec-butylamine
(Systematic) nomenclature of alkanes 1. Determine the number of carbons in the longest continuous chain. Ch 2 #12 longest continuous chain = parent C = root chain root+ane
Ch 2 #13 2. Number the chain so that the substituent gets the lowest number. #-[substituent][parent] no # in common name iso, sec-, tert- are common names; but accepted to IUPAC system when 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
6. If two or more longest chains of the same length, the parent is the chain with the greatest number of subs. Ch 2 #16
Ch 2 #17 7. For branched substituent, may use common name; iso, sec-, tert- much simpler 5-(2-methylpropan-1-yl)decane 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 skeletal structure = bond-line structure draw by drawing a line for a (C-C) bond not showing C and bonded to C Ch 2 #18 line(-bond) structure = Kekule structure C 3 3 C C3 C C 3 C C C C C C C C C C 2 C 2 C 3 C O C C C C C C O O OC 3 C 3 O O O
Cycloalkanes Ch 2 #19 cycloalkane ~ cyclic alkane ~ alkane in a ring, C n 2n 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 RO ~ with hydroxy [O] 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
IUPAC nomenclature for comp d with functional group # just before ol or before name Ch 2 #25 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 RN 2, RR N, 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 N 2 O 5-aminohexan-2-ol N triethylamine N,N-diethylethanamine quaternary ammonium salt
Structure of RX, ROR, RO, and RN 2 all sp 3 C, O, and N Ch 2 #30
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 betw on EN atom [N, O, F] and EN atom [N, O, F] fairly strong (3 8 kcal/mol) due to high EN and short distance (small ) on C? on Cl? strength the same? O- is a better -bond donor larger EN -N: is a better accepter more loose e pair δ+ δ (2.1) C(2.5) N(3.0) O(3.5) F(4.0) Cl(3.0)
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 R ~ low bp (1) only ROR ~ bp higher than R (2) RO ~ much higher bp (3) amines lower bp than RO relative -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] G mix = mix T S mix S mix > 0 always As Temp up, T S up mix depends on 1-2 interaction intermolecular interaction betw 1 and 2 like dissolves like {polar, hydrophilic, water-soluble} vs {nonpolar, hydrophobic, oil-soluble [organic]} R ~ nonpolar ~ water-insoluble floats on water ~ density of C30 < 1
Ch 2 #36 RO ~ water-solubility depends on size and shape of R propanol soluble with water; butanol not butyl alcohol less soluble than t-butyl alcohol O O ROR ~ less water-soluble than RO 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 -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- σ and C- σ* due to (the absence of) repulsion between C- 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 3 C C 3 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, (highly) strained
cyclopentane If planar, 108 bond angle (no angle strain) and eclipsed puckered to relieve torsional strain envelope little strained Ch 2 #46 cyclohexane If planar, 120 and fully eclipsed puckered to reduce angle and torsional strain chair comformation virtually strain free (110 and staggered)
Ch 2 #47 cycloheptane nonplanar a little higher (angle and torsional) strain than cx, close to cyclopentane rings betw C 8 C 11 very small angle and torsional strain transannular [cross-ring] strain (interior of the ring) arises similar total strain to those of C 5 and C 7, but not so popular rings larger than C 12 strain-free not popular
Drawing cx (chair) Ch 2 #48 3 pairs of parallel ring bonds 6 axial and 6 equatorial (subs) bonds axial hydrogen equatorial 4 5
Conformations of cx Ch 2 #49 chair and boat conformation Boat conformer is of higher strain torsional ~ 4 eclipsed steric ~ flagpole
Ring flip of cx Ch 2 #50 chair boat chair axial-equatorial change low E barrier ~ rapid equili of chairs twist-boat
Monosubstituted cx Ch 2 #51 methylcyclohexane C 3 C 3 2 chair conformations are not identical (in energy) axial-me-cx is of higher steric strain than equatorial-me-cx. due to 1,3-diaxial interactions C 3 5 1 3 1 2 3 Energy of 1,3-diaxial = E of 2 gauches = 2 x.87 = 1.74 kcal/mol
Equili favored to equatorial G = 1.74 kcal/mol = RT ln K K = exp [1.74/.6] = 18 at 300 K Prob(equatorial) = 18/(1+18) =.95 at 300 K C 3 K Ch 2 #52 C 3 C 2 C 3 C 3 C 3 Me Me Me frozen
Disubstituted cx Ch 2 #53 1,2-dimethylcyclohexane Me Me Me Me cis-trans isomers [geometric isomers] not conformers Each has conformers. different configuration need breaking bonds to change different compounds with different mp, bp, --- Me Me
Ch 2 #54 trans-1,2-me 2 cx is more stable. cis- trans-.87 x 3 = 2.6 kcal/mol.87 x 4 = 3.5 kcal/mol.87 kcal/mol
1,4-Me 2 cx trans-isomer is more stable. ~ fully explained in the textbook 1,3-Me 2 cx cis-isomer more stable ~ prove this by yourself 1-tert-butyl-3-methylcyclohexane Ch 2 #55
Fused rings Ch 2 #56 trans-fused rings are more stable. hormones, steroids, cholesterol