organic compounds alkanesand cycloalkanes
TRANSCRIPT
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
1/32
3. Organic Compounds:Alkanes and Cycloalkanes
Based on
McMurrys Organic Chemistry , 6th
edition, Chapter 3
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
2/32
2
Families of Organic Compounds
Organic compounds can be grouped into familiesby their common structural featuresWe shall survey the nature of the compounds in atour of the families in this course
This chapter deals with alkanes , compounds thatcontain only carbons and hydrogens, allconnected exclusively by single bonds
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
3/32
3
3.1 Functional Groups
Functional group - collection of atoms at a sitewithin a molecule with a common bonding patternThe group reacts in a typical way, generallyindependent of the rest of the moleculeFor example, the double bonds in simple and
complex alkenes react with bromine in the same way(See Figure 3.1)
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
4/32
4
Survey of Functional Groups
Table 3.1 lists a wide variety of functional
groups that you should recognize (also insideback cover)As you learn about them in each chapter itwill be easier to recognize themThe functional groups affect the reactions,structure, and physical properties of everycompound in which they occur
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
5/32
5
Types of Functional Groups: Multiple
CarbonCarbon Bonds* Alkenes have a C-C double bond* Alkynes have a C-C triple bond* Arenes have
special bonds thatare represented asalternating singleand double C-Cbonds in a six-membered ring
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
6/32
6
Functional Groups with Carbon Singly Bonded
to an Electronegative Atom* Alkyl halide: C bonded to halogen (C-X)
* Alcohol: C bonded O of a hydroxyl group (C-OH)* Ether: Two Cs bonded to the same O (C-O-C)* Amine: C bonded to N (C-N)
Thiol: C bonded to SH group (C-SH)S ulfide: Two Cs bonded to same S (C-S-C)Bonds are polar, with partial positive charge on C
( +) and partial negative charge ( ) onelectronegative atom
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
7/32
7
Groups with a CarbonOxygen Double Bond
(Carbonyl Groups)* Aldehyde: one hydrogen bonded to C=O
* Ketone: two Cs bonded to the C=O* Carboxylic acid: OH bonded to the C=O* Ester: C-O bonded to the C=OAmide: C-N bonded to the C=OAcid chloride: Cl bonded to the C=OCarbonyl C has partial positive charge ( +)Carbonyl O has partial negative charge ( -).
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
8/32
8
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
9/32
9
3.2 Alkanes and Alkane Isomers
Alkanes: Compounds with C-C single bonds and C-Hbonds only (no functional groups)Connecting carbons can lead to large or small moleculesThe formula for an alkane with no rings in it must beCnH2n+2 where the number of Cs is n
Alkanes are saturated with hydrogen (no more can beadded
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
10/32
10
Alkane Isomers
CH 4 = methane, C 2H6 = ethane, C 3H8= propane
The molecular formula of an alkane with more thanthree carbons can give more than one structureC4 (butane) = butane and isobutaneC
5(pentane) = pentane, 2-methylbutane, and 2,2-
dimethylpropane
Alkanes with Cs connected to no more than 2 other Cs are straight-chain (continuous-chain ) or normal alkanesAlkanes with one or more Cs connected to 3 or 4 Csare branched-chain alkanes
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
11/32
11
Constitutional Isomers
Isomers that differ in how their atoms are arranged inchains are called constitutional isomersCompounds other than alkanes can beconstitutional isomers of one another They must have the same molecular formula to be
isomers
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
12/32
12
Condensed Structures of Alkanes
We can represent an alkane in a brief form or inmany types of extended formA condensed structure does not show bonds but listsatoms, such as
CH 3CH 2CH 3 (propane)
CH 3C(CH 3)2CH 3 (2,2-dimethylpropane)
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
13/32
13
Names of Small Hydrocarbons
No. of Carbons Formula Name (C n H2n +2)
1 Methane CH 42 Ethane C 2H63 Propane C 3H84 Butane C
4H
105 Pentane C 5H126 Hexane C 6H147 Heptane C
7H
168 Octane C 8H189 Nonane C 9H20
10 Decane C 10 H22
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
14/32
14
Problem 3.4 Five isomers of C 6H14 .
3.5 a. two esters of C 5H10 O 2b two nitriles of C 4H7N
3.6 How many isomersa. Alcohols of C 3H8Ob. Bromoalkanes of C
4H
9Br
C10 H22 has 75 isomers
C 20 H42 has over 360,000
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
15/32
15
3.3 Alkyl Groups
Alkyl group remove one H from an alkane(a part of a structure)General abbreviation R (for Radical, anincomplete species or the rest of the
molecule)Name: replace - ane ending of alkane with - yl ending
CH 3 is methyl (from methane)CH 2CH 3 is ethyl from ethane
See Table 3.4 for a list
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
16/32
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
17/32
17
You must know:
One methyl groupOne ethyl groupTwo propyl groupsFour butyl groups (common names)
iso- means methyl branch secondfrom far end of chain.
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
18/32
18
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
19/32
19
3.4 Naming Alkanes (IUPAC)
Compounds are given systematic names by aprocess that uses
Prefix-Parent-SuffixFollows specific rules
Named as longest possible chain
If two possibilities-chose one with more branchesCarbons in that chain are numbered in sequenceSubstituents are numbered at their point of attachment
Compound name is one word (German style)Complex substituents are named as compounds wouldbe
See specific examples in text
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
20/32
20
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
21/32
21
The IUPAC rules can be very complex,but each organic compound can be assigneda unique name, and from the name thestructure can be written. See appendix A.
Many organic compounds are known bytheir common or trivial name especially
if they are complex. These frequently give noclue as to the structure.
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
22/32
22
3.5 Properties of Alkanes
Called paraffins (low affinity compounds)because they undergo few types of reactionsThey will burn in a flame, producing carbondioxide, water, and heat
They react with Cl 2 in the presence of light toreplace Hs with Cls (not controlled)
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
23/32
23
Physical Properties
Boiling points and melting points increase as size of alkane increasesForces between molecules (temporary dipoles,dispersion) are weak
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
24/32
24
Problems from Chapter 3Pages 93-101
21-36, 39, 42-47, 49-54
OWL for chap 3Sept 22
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
25/32
25
3.6 Cycloalkanes
Cycloalkanes are alkanes that have carbon atomsthat form a ring (called alicyclic compounds)
Simple cycloalkanes rings of CH2 units, (CH2) n ,or C n H2 n Structure is shown as a regular polygon with thenumber of vertices equal to the number of Cs (aprojection of the actual structure)
cyclopropanecyclohexanecyclopentane
cyclobutane
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
26/32
26
Complex Cycloalkanes
Naturally occurring materials contain cycloalkane structuresExamples: chrysanthemic acid (cyclopropane),
prostaglandins (cyclopentane), steroids (cyclohexanes andcyclopentane)
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
27/32
27
Properties of Cycloalkanes
Melting points are affected by the shapes and theway that crystals pack so they do not change
uniformly
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
28/32
28
3.7 Naming Cycloalkanes
Count the number of carbon atoms in the ring and the number inthe largest substituent chain. If the number of carbon atoms inthe ring is equal to or greater than the number in the substituent,the compound is named as an alkyl-substituted cycloalkaneFor an alkyl- or halo-substituted cycloalkane, start at a point of attachment as C1 and number the substituents on the ring sothat the second substituent has as low a number as possible.Number the substituents and write the nameSee text for more details and examples
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
29/32
29
3 8 Ci T I i i
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
30/32
30
3.8 Cis-Trans Isomerism in
CycloalkanesRotation about C-C bonds in cycloalkanes is limited by thering structure
Rings have two faces and substituents are labeled as totheir relative facial positionsThere are two different 1,2-dimethyl-cyclopropaneisomers, one with the two methyls on the same side (cis)of the ring and one with the methyls on opposite sides(trans)
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
31/32
31
Stereoisomers
Compounds with atoms connected in the same order but whichdiffer in three-dimensional orientation, are stereoisomersThe terms cis and trans should be used to specifystereoisomeric ring structuresRecall that constitutional isomers have atoms connected indifferent order
-
8/6/2019 Organic Compounds Alkanesand Cycloalkanes
32/32
32