Lecture Slides on Organic Compounds: Alkanes and Cycloalkanes | CHEM 2010, Study notes of Organic Chemistry

Download Lecture Slides on Organic Compounds: Alkanes and Cycloalkanes | CHEM 2010 and more Study notes Organic Chemistry in PDF only on Docsity! 3. Organic Compounds: Alkanes and Cycloalkanes Based on McMurry’s Organic Chemistry, 6th edition, Chapter 3 2 Families of Organic Compounds  Organic compounds can be grouped into families by their common structural features  We shall survey the nature of the compounds in a tour of the families in this course  This chapter deals with alkanes, compounds that contain only carbons and hydrogens, all connected exclusively by single bonds Double Bond as Functional Group OH CH3 H ~ Cx Cy H H \ Reaction site ————»> Double bond 6 Survey of Functional Groups  Table 3.1 lists a wide variety of functional groups that you should recognize  As you learn about them in each chapter it will be easier to recognize them  The functional groups affect the reactions, structure, and physical properties of every compound in which they occur 7 Types of Functional Groups: Multiple Carbon–Carbon Bonds  Alkenes have a C-C double bond  Alkynes have a C-C triple bond  Arenes (or aromatic hydrocarbons) have special bonds that are represented as alternating single and double C- C bonds in a six-membered ring Alkyl halide Alcohol Ether Amine (haloalkane) ©2004 Thomson - Brooks/Cole 11 Groups with a Carbon–Oxygen Double Bond (Carbonyl Groups)  Aldehyde: one hydrogen bonded to C=O  Ketone: two C’s bonded to the C=O  Carboxylic acid: OH bonded to the C=O  Ester: C-O bonded to the C=O  Amide: C-N bonded to the C=O  Acid chloride: Cl bonded to the C=O  Carbonyl C has partial positive charge (+) and partial negative charge ()  Carbonyl O has partial negative charge (-). 6-— O I ss He vow JH C C 4s 4% H HH H Acetone—a typical carbonyl compound ©2004 Thomson - Brooks/Cole oO 0 0 i oP “oe “Hy “eo “ee “ae OH “ \ ‘ €% Aldehyde Ketone Carboxylic acid ©2004 Thomson - Brooks/Cole 0 oO 10) Loy i fy | “y Ester Amide Acid chloride  A “saturated” fat (glyceryl stearate): O | CH,OCCH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH, oO | CHOCCH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH, CH,OCCH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH,CH; A typical animal fat ©2004 Thomson - Brooks/Cole 15 16 Alkane Isomers  CH4 = methane, C2H6 = ethane, C3H8= propane  The molecular formula of an alkane with more than three carbons can give more than one structure  C4 (butane) = butane and isobutane  C5 (pentane) = pentane, 2-methylbutane (isopentane), and 2,2-dimethylpropane (neopentane) 'Methane, ethane, & propane A —— H Methane, CH, ©2004 Thomson - Brooks/Cole Be yy ii , ¥ H— = ja H H— 5 b= = H HOH HoH OH Ethane, C2H, Propane, C3H, 17  Alkane Isomers TABLE 3.2 Number of Alkane Isomers Number Formula of isomers CoH, 5 C7Hi¢ a CsgHig 18 CoHoo0 35 CioH22 75 Ci5H32 4,347 CopH yo 366,319 CsoHo2 ©2004 Thomson - Brooks/Cole 4,111,846,763 20 21 Alkane Isomers  Alkanes with C’s connected to no more than 2 other C’s are straight-chain or normal alkanes  Alkanes with one or more C’s connected to 3 or 4 C’s are branched-chain alkanes 22 Constitutional (Structural) Isomers  Isomers that differ in how their atoms are arranged in chains are called constitutional (or structural) isomers  Compounds other than alkanes can be constitutional isomers of one another  They must have the same molecular formula to be isomers Condensed Structures of Alkanes HHH #H H HH 4H | | \ 7 \/ a7 qe ee J\ Ff H H H H H HH HB CH,;—CH,—CH,— CH, CH,CH,CH,CHs CH,(CH,)2CHg © 2004 Thomson/Brooks Cole 25 26 Names of Small HydrocarbonsNo. of Carbons Formula Name (CnH2n+2) 1 Methane CH4 2 Ethane C2H6 3 Propane C3H8 4 Butane C4H10 5 Pentane C5H12 6 Hexane C6H14 7 Heptane C7H16 8 Octane C8H18 9 Nonane C9H20 10 Decane C10H22 27 3.3 Alkyl Groups  Alkyl group – remove one H from an alkane (a part of a structure)  General abbreviation “R” (for Radical, an incomplete species or the “rest” of the molecule)  Name: replace -ane ending of alkane with - yl ending  CH3 is “methyl” (from methane)  CH2CH3 is “ethyl” from ethane AV CH;CH2CHsCHs; CH,CH,CH,CH,-- and CH;CH,CHCH3 Butane Butyl sec-Butyl C44 CH; CH; CH; | | | CH,CHCH; CH,;CHCH,= and Ee Isobutane Isobutyl CH; tert-Butyl © 2004 Thomson/Brooks Cale 30 31 Types of Alkyl groups  a carbon at the end of a chain (primary alkyl group)  a carbon in the middle of a chain (secondary alkyl group)  a carbon with three carbons attached to it (tertiary alkyl group) Types of Alkyl groups | R—C—H H Primary carbon (1Y) — Secondary carbon (2\) is bonded to one other carbon © Thomson - Brooks Cole H R-U-i | R is bonded to two other carbons R-C—Hi | R | —_— R Tertiary carbon (3)) is bonded to three other carbons R—C—R | R Quaternary carbon (4) is bonded to four other carbons 32  Problem 3.8: Primary, secondary, tertiary, or quaternary carbons? CH, CH THOR | (a) CH,;CHCH,CH,CH, (b) CH;CH,CHCH,CH, ©2004 Thomson - Brooks/Cole CH, CH, | (c) CH,CHCH,OCH, CH, 35 36 3.4 Naming Alkanes: IUPAC  Compounds are given systematic names by a process that uses: 37 3.4 Naming Alkanes: IUPAC Follows specific rules:  Named as longest continuous chain of C’s  Carbons in that chain are numbered in sequence  Substituents are numbered at their point of attachment  Compound name is one word (German style)  Complex substituents are named similarly 9 8 CH,CH, CHs BaEs CHCH,CH,CH— CHCH,CHs Named as a nonane 3. Identify “" Substituents: On C3,CH,CH, (3-ethyl) & number On C4, CH; (4-methyl) On C7, CH, (7-methyl) th e ©2004 Thomson - Brooks/Cole substituent CH, | S CH;CHs—, a GHGs Named as a hexane ie CH; CH; Substituents: On 02, CH; (2-methyl) On C4, CH; (4-methyl) On C4, CH,CH; (4-ethyl) (©2004 Thomson - Brooks/Cole 40  4. Write the name CH, 4 9 38 | CH,CH, CH,CH, ty my CHsCHCHCH,CH;CH, 6 5 4 38 T 8 & 4 oS CH,CH,CH,CH— CH, CH,—CHCH,CH,CH—CHCH,CH, CH,CH, 3-Methylhexane 3-Ethyl-4,7-dimethylnonane 3-Ethyl-2-methylhexane ©2004 Thomson - Brooks/Cole 1CH; CH; é. 5 le 9 2 1 2CH CH;CH,— ) eet eed CHs— CHCH— CH,CHs ai CH; CH,CH,CHs CH; 4-Ethy1-3-methylheptane 4-Ethy1-2,4-dimethylhexane ©2004 Thomson - Brooks/Cole 41  Practice prob. 3.2: IUPAC name? CH,CH, CH, | | CH,CHCH,CH,CH,CHCH;  Solution: Ca Hee CH;CHCHCH,CH,CH; _3-Isopropyl-2-methylhexane CH, ©2004 Thomson - Brooks/Cole 45  Problem 3.11: IUPAC names? CH; (a) The three isomers of C,H. (b) 5 CH,CH, f f (c) (CH;),CHCH,CHCH, (d) ie CH,CH, ©2004 Thomson - Brooks/Cole 46 47 Problem 3.39: Draw structures 1. 2-methylheptane 2. 4-ethyl-2,2-dimethylhexane 3. 4-ethyl-3,4-dimethyloctane 4. 2,4,4-trimethylheptane 5. 3,3-diethyl-2,5-dimethylnonane 6. 4-isopropyl-3-methylheptane 50 Physical Properties  Boiling points and melting points increase as size of alkane increases  Forces between molecules (temporary dipoles, dispersion) are weak Physical Properties 300 5 | | Melting point Bi Boiling point 200 - 8 a e 100- 3 5 — fos a + —100 + i 2 3 4 5 6 7 8 gi Number of carbons © Thomson - Brooks Cole 10 11 12 13 14 51 52 3.6 Cycloalkanes  Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds)  Simple cycloalkanes are rings of CH2 units, (CH2)n, or CnH2n  Structure is shown as a regular polygon with the number of vertices equal to the number of C’s (a projection of the actual structure) Complex Cycloalkanes Ho H H OH ‘© Thomson - Brooks Cole HC CHs Cortisone ee --H / H CO.H 55 56 Properties of Cycloalkanes  Melting points are affected by the shapes and the way that crystals pack so they do not change uniformly 57 3.7 Naming Cycloalkanes  Count the number of carbon atoms in the ring and the number in the largest substituent chain. If the number of carbon atoms in the ring is equal to or greater than the number in the substituent, the compound is named as an alkyl-substituted cycloalkane  For an alkyl- or halo-substituted cycloalkane, start at a point of attachment as C1 and number the substituents on the ring so that the second substituent has as low a number as possible.  Number the substituents and write the name Examples: 2-CH; 1“Br 1-Bromo-2-methylcyclobutane ©2004 Thomson - Brooks/Gole CH,CH; 1-Bromo-3-ethyl-5-methyl- cyclohexane ©2004 Thomson - Brooks/Cole NOT CH, | CHCH,CH, (1-Methylpropyl)cyclobutane (or sec-Butyleyclobutane) CH, 2*“Br 2-Bromo-1-methylcyclobutane cl \ CH, 2 CH,CH, 1-Chloro-3-ethyl-2-methyl- cyclopentane 60  Problem 3.15: IUPAC names? (a) CH; (b) CH,CH,CH; (ce) a Se CH, CH,CH, —(e) or (f) Br CH(CH,), Br C(CHs)s ©2004 Thomson - Brooks/Cole (d) 61 62 3.8 Cis-Trans Isomerism in Cycloalkanes  Rotation about C-C bonds in cycloalkanes is limited by the ring structure  Rings have two “faces” and substituents are labeled as to their relative facial positions  There are two different 1,2-dimethyl-cyclopropane isomers, one with the two methyls on the same side (cis) of the ring and one with the methyls on opposite sides (trans) Stereoisomers Constitutional isomers CH; (different connections | between atoms) CH;— CH— CH; Stereoisomers H3C CHs3 (same connections XX but different three- H H dimensional geometry) © Thomson - Brooks Cole cis-1,3-Dimethylcyclobutane © Thomsén - Brooks Cole and CH,—CH,—CH,—CH, H,C H and \ H CH; Br 5 4 H << H CH,CH, trans-1-Bromo-3-ethylcyclopentane 65  Practice Prob. 3.4: Name? ©2004 Thomson - Brooks/Cole 66  Problem 3.18: IUPAC Name? yeh Ho \-H cls H ©2004 Thomson - Brooks/Cole 67