1-1 CHEM 121, Winter 2009, LA TECH Chapter 12. Saturated Hydrocarbons Sections.

1-1CHEM 121, Winter 2009, LA CHEM 121, Winter 2009, LA TECHTECH

Chapter 12. Saturated Hydrocarbons

SectionsSections


12.1 Organic and Inorganic Compounds12.1 Organic and Inorganic Compounds12.2 Bonding Characteristics of the Carbon Atom12.2 Bonding Characteristics of the Carbon Atom12.3 Hydrocarbons and Hydrocarbon Derivatives12.3 Hydrocarbons and Hydrocarbon Derivatives12.4 Alkanes: Acyclic Saturated Hydrocarbons12.4 Alkanes: Acyclic Saturated Hydrocarbons12.5 Structural Formulas12.5 Structural Formulas12.6 Alkane Isomerism12.6 Alkane Isomerism12.7 Conformations of Alkanes12.7 Conformations of Alkanes12.8 IUPAC Nomenclature for Alkanes12.8 IUPAC Nomenclature for Alkanes12.9 Line-Angle Formulas for Alkanes12.9 Line-Angle Formulas for Alkanes12.10 Classification of Carbon Atoms12.10 Classification of Carbon Atoms12.11 Branched-Chain Alkyl Groups12.11 Branched-Chain Alkyl Groups12.12 Cycloalkanes12.12 Cycloalkanes12.13 IUPAC Nomenclature for Cycloalkanes12.13 IUPAC Nomenclature for Cycloalkanes12.14 Isomerism in Cycloalkanes12.14 Isomerism in Cycloalkanes12.15 Sources of Alkanes and Cycloalkanes12.15 Sources of Alkanes and Cycloalkanes12.16 Physical Properties of Alkanes and Cycloalkanes12.16 Physical Properties of Alkanes and Cycloalkanes12.17 Chemical Properties of Alkanes and Cycloalkanes12.17 Chemical Properties of Alkanes and CycloalkanesChemistry at a Glance: Properties of Alkanes and Chemistry at a Glance: Properties of Alkanes and Cycloalkanes Cycloalkanes


IntroductionIntroduction

Organic chemistryOrganic chemistry is the study of the compounds of is the study of the compounds of carbon atoms consisting of single, double, and carbon atoms consisting of single, double, and triple covalent bonds with C, H, O, N, and some triple covalent bonds with C, H, O, N, and some metalsmetals

BiochemistryBiochemistry is the study of the compounds of is the study of the compounds of carbon atoms consisting of single, double, and carbon atoms consisting of single, double, and triple covalent bonds with C, H, O, N, and some triple covalent bonds with C, H, O, N, and some metalsmetals


12.1 Organic and Inorganic Compounds12.1 Organic and Inorganic Compounds


SectionsSectionsChapter 1: Covalent Bonding and Shapes of MoleculesChapter 1: Covalent Bonding and Shapes of Molecules

1.1. IntroductionIntroduction

2.2. Electronic Structure of atomsElectronic Structure of atoms

3.3. Lewis Model of bondingLewis Model of bonding

4.4. Bond angles and molecular shapesBond angles and molecular shapes

5.5. Polar and non-polar moleculesPolar and non-polar molecules

6.6. ResonanceResonance

7.7. Orbital overlap of covalent bondingOrbital overlap of covalent bonding

8.8. Functional groupsFunctional groups


IntroductionIntroduction

Organic chemistryOrganic chemistry is the study of the compounds of is the study of the compounds of carbon. carbon.

C is a small atomC is a small atom • it forms four bonds consisting of single, double, it forms four bonds consisting of single, double,

and triple bondsand triple bonds• it forms strong bonds with C, H, O, N, and some it forms strong bonds with C, H, O, N, and some

metalsmetals

ProblemProblem: Identify : Identify organicorganic and and inorganicinorganic compounds:compounds:

NaCl, CNaCl, C22HH55OH, CHOH, CH33COOH, NaCOOH, Na22COCO33, CH, CH33OK, KOHOK, KOH


Atomic OrbitalsAtomic Orbitals

s orbitals orbital - a spherical-shaped atomic orbital; can - a spherical-shaped atomic orbital; can hold a maximum of 2 electronshold a maximum of 2 electrons

p orbitalp orbital - a dumbbell-shaped atomic orbital; the - a dumbbell-shaped atomic orbital; the three p orbitals (pthree p orbitals (pxx, p, pyy, p, pzz) can hold a maximum ) can hold a maximum of 2 electrons eachof 2 electrons each

Electrons always fill starting with the lowest-energy Electrons always fill starting with the lowest-energy orbital:orbital:

lower energylower energy higher energyhigher energy1s1s22 2s2s22 2p2p66 3s3s22 3p3p66

We will be concerned with only the valence We will be concerned with only the valence electrons which are the outermost electrons electrons which are the outermost electrons involved in forming bonds. involved in forming bonds.


Shapes of s Atomic OrbitalsShapes of s Atomic OrbitalsAll All ss orbitals have the shape of a sphere, with orbitals have the shape of a sphere, with

its center at the nucleus its center at the nucleus • of the s orbitals, a 1s orbital is the smallest, a 2s

orbital is larger, and a 3s orbital is larger still


Shapes of p Atomic OrbitalsShapes of p Atomic Orbitals• A p orbital consists of two lobes arranged in a

straight line with the center at the nucleus


Electronic Structure of atoms (Review)Electronic Structure of atoms (Review)Ground state electronic configuration of atoms in core formatGround state electronic configuration of atoms in core format

Carbon (C): ):Carbon (C): ): [He] [He] 22ss22, 2, 2pp2 2

oror [He][He] 2 2ss22, 2p, 2pxx113p3pyy

113p3pzz00

Potassium (K): Potassium (K): {Ar] {Ar] 44ss11

Phosphorous (P):Phosphorous (P): [Ne] [Ne] 33ss22, 3, 3pp33

Valence shell electronic configurationValence shell electronic configuration

Carbon (C): ):Carbon (C): ): 33ss22, 3, 3pp22

Potassium (K): Potassium (K): 44ss11

Phosphorous (P):Phosphorous (P): 33ss22, 3, 3pp33

How you get the electronic configuration of an atom from the How you get the electronic configuration of an atom from the periodic table?periodic table?


Excited State Valence Electron ConfigurationExcited State Valence Electron Configuration

Carbon (C):Carbon (C):

Ground state:Ground state: 22ss22, 2, 2pp2 2 or or 22ss22, 2p, 2pxx113p3pyy

113p3pzz00

Excited State:Excited State: 22ss11, 2, 2pp3 3 or or 22ss11, 2p, 2pxx113p3pyy

113p3pzz11

1s2 2s2 2p2

E

1s2 2s1 2p3

electronpromotion


Lewis Model of bonding (Review)Lewis Model of bonding (Review)

"octet rule“"octet rule“atoms tend to gain, lose or share electrons so as to atoms tend to gain, lose or share electrons so as to

have eight electrons in their outer electron shell have eight electrons in their outer electron shell ““Lewis structure of atoms”Lewis structure of atoms” Shows only valence electrons, is a convenient way Shows only valence electrons, is a convenient way

of representing atoms to show their chemical of representing atoms to show their chemical bonding pattern. bonding pattern.


Lewis structure of atoms (Review)Lewis structure of atoms (Review)


CC

NN

NaNa++

OO

Cations•What elements lose electrons? And how many?•What is the positive charge on their cations?•Anions•What elements gain electrons?•What is the positive charge on their anions?•Covalent bonds•How many covalent bonds are formed? •What elements share electrons?

Cations and AnionsCations and Anions


Covalent or IonicCovalent or IonicIdentify Identify covalent covalent and and ionicionic compounds: compounds:

NaCl, CNaCl, C22HH55OH, CHOH, CH33COOH, NaCOOH, Na22COCO33, CH, CH33OK, KOHOK, KOH

Covalent :Covalent :

Ionic:Ionic:


Ionic model of bonding modelIonic model of bonding model (Review)(Review)

+ -Na + F Na F

Ionic bondIonic bond - results from the - results from the electrostatic attractionelectrostatic attraction

between a cation and an anion of two atoms typically between a cation and an anion of two atoms typically

involves a involves a metalmetal and a and a nonmetallic element.nonmetallic element.

Anion:Anion: An atom that gains electrons becomes a negative

ion

CationCation: An atom that loses electrons becomes a positive

ion

+ 2-Li + S 2 Li S2


Covalent model of bondingCovalent model of bonding (Review)(Review)

Covalent bondsCovalent bonds - results from the sharing of electrons - results from the sharing of electrons between two atoms typically involves two between two atoms typically involves two nonmetallic elementsnonmetallic elements


HH

2.12.1

LiLi Be Be BB CC NN OO FF

1.01.0 1.51.5 2.02.0 2.52.5 3.03.0 3.53.54.04.0

NaNa MgMg AlAl SiSi PP SS ClCl

0.90.9 1.21.2 1.51.5 1.81.8 2.12.1 2.52.53.03.0

increases

increases

Is the attraction of an atom for its valence electronsIs the attraction of an atom for its valence electrons

Electronegativity (Review)Electronegativity (Review)


Nonpolar/polar-covalent and ionic bonds. (Review)Nonpolar/polar-covalent and ionic bonds. (Review)

We classify chemical bonds as We classify chemical bonds as polar polar covalent, nonpolar covalent, nonpolar covalentcovalent and and ionicionic based on the difference in based on the difference in electronegativity between the atomselectronegativity between the atoms

Difference in ElectronegativityBetween Bonded Atoms Type of Bond

less than 0.5

0.5 to 1.9greater than 1.9

nonpolar covalentpolar covalent

ionic


Classify following bonds nonpolar-covalent, Classify following bonds nonpolar-covalent, polar-covalent or ionic bonds polar-covalent or ionic bonds

N-H N-H nonpolar-covalent, polar-covalent or ionic bondsnonpolar-covalent, polar-covalent or ionic bonds

O-H O-H nonpolar-covalent, polar-covalent or ionic bondsnonpolar-covalent, polar-covalent or ionic bonds

C-H C-H nonpolar-covalent, polar-covalent or ionic bondsnonpolar-covalent, polar-covalent or ionic bonds

C-F C-F nonpolar-covalent, polar-covalent or ionic bondsnonpolar-covalent, polar-covalent or ionic bonds

Na-Cl Na-Cl nonpolar-covalent, polar-covalent or ionic bondsnonpolar-covalent, polar-covalent or ionic bonds

Al-Cl Al-Cl nonpolar-covalent, polar-covalent or ionic bondsnonpolar-covalent, polar-covalent or ionic bonds


Drawing Lewis structure molecules and ionsDrawing Lewis structure molecules and ions (Review)(Review) 1)1) Predict arrangement of atoms.Predict arrangement of atoms.

a) H is always a terminal atom.

b) Halogens and oxygen are often terminal.

c) The central atom of binary compounds is usually written

d) first and has the lowest subscript.

e) Most organic compounds have more than two central atoms.

f) These are mainly C, but N, O and S can also be central atoms.

2) 2) TotalTotal number of valence electrons (e-) number of valence electrons (e-)

a) Add all valence electron of atoms in the molecule from the formula.

b) Add the ion charge for negative ions or subtract for positive ions.


Drawing Lewis structure molecules and ions Drawing Lewis structure molecules and ions (Review)(Review) 3)3) Draw the skeletal structure by connecting the atoms with Draw the skeletal structure by connecting the atoms with

single bonds.single bonds.

4) 4) Give each of the atoms an octet (8 e-). Adding unshared Give each of the atoms an octet (8 e-). Adding unshared pairs of electronspairs of electrons

5) 5) Count the total number of e- used through step 4 and Count the total number of e- used through step 4 and compare to the number calculated incompare to the number calculated in step 2. step 2.

a)a) If it results in zero, the structure is correct. If it results in zero, the structure is correct.

b)b) For every two electrons too many, another bond is added For every two electrons too many, another bond is added (minimize formal charges). (minimize formal charges).

Multiple bonds form only with C, N, O and S.Multiple bonds form only with C, N, O and S.

Total number of bonds to neutral atoms:Total number of bonds to neutral atoms: 4 bonds to C 3 bonds to N, P 2 bonds to O, S 1 bond to H, F, Cl, Br, I


Calculation of formal charges of atoms in the Lewis structureCalculation of formal charges of atoms in the Lewis structure

1.1. For a neutral molecule, the sum of the formal charges equals zero. For For a neutral molecule, the sum of the formal charges equals zero. For

a polyatomic ion, the sum of the formal charges equals the charge on a polyatomic ion, the sum of the formal charges equals the charge on

the ion.the ion.

2.2. Formal charge of each atom is calculated by:Formal charge of each atom is calculated by:

(group #) - (# unshared e-) - (group #) - (# unshared e-) - ½½ (# shared e-) (# shared e-)

3.3. Formal charges are shown as + or - on the atom with that charge.Formal charges are shown as + or - on the atom with that charge.

4.4. An atom with the same number of bonds as its group number has no An atom with the same number of bonds as its group number has no

formal charge.formal charge.

5.5. In a molecule if two different elements can be assigned a negative In a molecule if two different elements can be assigned a negative

charge, then the more electronegative element gets the charge; the charge, then the more electronegative element gets the charge; the

same sign should not be given to bonded atoms.same sign should not be given to bonded atoms.


Types of electronsTypes of electrons

Bonding pairsBonding pairsTwo electrons that are Two electrons that are sharedshared between two atoms. between two atoms. A covalent bond.A covalent bond.

Unshared (nonbonding ) pairsUnshared (nonbonding ) pairs A pair of electrons that are not shared between two A pair of electrons that are not shared between two

atoms. atoms. Lone pairsLone pairs or nonbonding electrons. or nonbonding electrons.

H Cloo

oo

oooo

Bonding pair

Unsharedpair


Lewis StructuresLewis Structures (Review)(Review)

Hydrogen chloride

Methane Ammonia

Water

H O

H

H

H NH C

H

H

H Cl

H

H

H2O (8)

NH3 (8)CH4 (8)

HCl (8)

•How many bonding electron pairs are in the molecule?

•How many bonding electron pairs are in each atom?

•How many nonbonding electron pairs are in the molecule?


Draw Lewis structure of moleculesDraw Lewis structure of molecules

CHClCHCl33

CC22HH44

CC33HH88OO

CHCH33CHCH22CHCH22OHOH

CHCH33CHCH22OCHOCH33

CHCH33COCO22HH

CHCH33CHOCHO


Draw Lewis structure and assign formal chargesDraw Lewis structure and assign formal charges

CHCH33NHNH33++

CHCH33OO--

C N

H

H

H

H

H

H

+


VValence-alence-SShell hell EElectron-lectron-PPair air RRepulsion epulsion (VSEPR) model(VSEPR) model (Review)(Review)

For predicting shapes of molecules and polyatomic Ions For predicting shapes of molecules and polyatomic Ions

based on the repulsion of valence pairs of electrons based on the repulsion of valence pairs of electrons

making them as far apart as possible around an making them as far apart as possible around an

atom of a Lewis structure.atom of a Lewis structure.

1) Draw the Lewis structure for the molecule or ion.1) Draw the Lewis structure for the molecule or ion.

2) Determine the number of bonding and unshared pairs attached to 2) Determine the number of bonding and unshared pairs attached to

the central atom.the central atom.

One single, double or triple bond counted as a bonding pairOne single, double or triple bond counted as a bonding pair

3) Choose the appropriate case from the given chart.3) Choose the appropriate case from the given chart.


Predict the bond angles of molecules from their Lewis Predict the bond angles of molecules from their Lewis structures. (Review)structures. (Review)

MoleculeMolecule Bonding pairsBonding pairs unshared unshared pairspairs

ShapeShape

HH22OO twotwo twotwo bentbent

NHNH33 threethree oneone Trigonal pyramidTrigonal pyramid

CHCH22OO threethree nonenone Trigonal planarTrigonal planar

CHClCHCl33 fourfour nonenone tetrahedraltetrahedral

CHCH44 fourfour nonenone tetrahedraltetrahedral

CClCCl44 fourfour nonenone tetrahedraltetrahedral


Polar and nonpolar moleculesPolar and nonpolar molecules

-

+

Insert elpot ofammonia(page 19)

Insert elpot offormaldehyde(page 20)

H HN

-

+H HC

O

Formaldehyde(polar)

HAmmonia

(polar)

H C C H

Insert elpot ofacetylene(page 20)

Acetylene(nonpolar)


Molecular Shape and Polarity Molecular Shape and Polarity (Review)(Review)

MoleculeMolecule Bonding pairs and Bonding pairs and unshared pairsunshared pairs

Electron pair Electron pair distributiondistribution

PolarityPolarity

HH22OO fourfour asymmetricasymmetric polarpolar

NHNH33 fourfour asymmetricasymmetric polarpolar

CHCH22OO threethree asymmetricasymmetric polarpolar

CHClCHCl33 fourfour asymmetricasymmetric polarpolar

CHCH44 fourfour symmetricsymmetric Non-polarNon-polar

CClCCl44 fourfour symmetricsymmetric Non-polarNon-polar


Curved arrow Electron pushingCurved arrow Electron pushing

Curved arrowCurved arrow:: a symbol used to show the a symbol used to show the redistribution of valence electronsredistribution of valence electrons

In using curved arrows, there are only two In using curved arrows, there are only two allowed types of electron redistribution:allowed types of electron redistribution:• from a bond to an adjacent atom• from an atom to an adjacent bond

Electron pushing by the use of curved arrows is Electron pushing by the use of curved arrows is also used in explaining reaction mechanismsalso used in explaining reaction mechanisms


Drawing Curved ArrowsDrawing Curved ArrowsTo show the movement of electrons in breaking and forming To show the movement of electrons in breaking and forming bonds. The bonds. The tail tail of the arrow is started at the site of electron of the arrow is started at the site of electron density (negative character such as a pi bond or density (negative character such as a pi bond or lone pairlone pair of of electrons) and proceeds to the arrowhead which is drawn to electrons) and proceeds to the arrowhead which is drawn to the site of electron deficiency (positive character). the site of electron deficiency (positive character). NEGATIVE TO POSITIVE!NEGATIVE TO POSITIVE!

Arrows can be drawn from:

1) lone pair

bond

2) bond lone pair

3) bond

bond

tail head


ResonanceResonance

For many molecules and ions with double For many molecules and ions with double bonds, two or more Lewis structure could be bonds, two or more Lewis structure could be writtenwritten


Orbital Overlap ModelOrbital Overlap Model


Hybrid Atomic OrbitalsHybrid Atomic Orbitals

Hybridization is the mixing up of two or more atomic orbitals

There are three types of hybrid atomic orbitals for There are three types of hybrid atomic orbitals for carboncarbonspsp33 (one s orbital + three p orbitals give four sp3

orbitals)spsp22 (one s orbital + two p orbitals give three sp2

orbitals)spsp (one s orbital + one p orbital give two sp orbitals)


Four spFour sp33 hybrids hybrids

Three spThree sp22 hybrids hybrids

Two spTwo sp hybrids hybrids

s and p hybridss and p hybrids


and and bonds bondsOverlap of hybrid orbitals can form two types Overlap of hybrid orbitals can form two types

of bonds, depending on the geometry of the of bonds, depending on the geometry of the overlapoverlap bondsbonds are formed by “direct” overlap

bondsbonds are formed by “parallel” overlap of unhybrid p prbitlas

s1 s1 p1 p1 s1 p1


and and bonds in single and multiple bonds bonds in single and multiple bonds

single bondsingle bond - one shared pair of electrons between - one shared pair of electrons between two atoms; a two atoms; a bond bond

double bonddouble bond - two shared pairs of electrons - two shared pairs of electrons between two atoms; one s bond and one between two atoms; one s bond and one bond bond

triple bondtriple bond - three shared pairs of electrons - three shared pairs of electrons between two atoms; one s bond and two p bondsbetween two atoms; one s bond and two p bonds


Bond PropertiesBond Properties

Bond strengthBond strength::

strongeststrongest weakest weakest

Bond lengthBond length::

longest shortestlongest shortest

C C C C C C> >

C CC CC C > >


Counting Counting and and bonds in Lewis structure bonds in Lewis structure

H-C-C-HH

H

H

H

H

C C

H

H H

H-C C-H

Hybrid-ization

Types of Bonds to Carbon Example

sp3 four sigma bonds

sp2 three sigma bondsand one pi bond

sp two sigma bondsand two pi bonds

Ethane

Ethylene

Acetylene

Name


Predicting hybridization of atoms in a Lewis Predicting hybridization of atoms in a Lewis structurestructure

Count sigma bonds and unshared electrons around Count sigma bonds and unshared electrons around the atomthe atomIf the total number of pairs:

2 sp hybridization

3 sp2 hybridization

4 sp3 hybridization


Functional Groups in Organic CompoundsFunctional Groups in Organic Compounds

Functional groupFunctional group:: an atom or group of atoms within a an atom or group of atoms within a molecule that shows a characteristic set of physical and molecule that shows a characteristic set of physical and chemical propertieschemical properties

Functional groupFunctional group• divide organic compounds into classes• the sites of characteristic chemical reactions• the basis for naming organic compounds


AlcoholAlcohol(carbon, hydrogen and (carbon, hydrogen and oxygen)oxygen)

CHCH33-CH-CH

22--OHOH

Thiol Thiol (thioalcohol) thio means (thioalcohol) thio means sulfursulfur

CHCH33-CH-CH

22-SH-SH

AmineAmine CHCH33-CH-CH

22-NH-NH22

EtherEther CHCH33-CH-CH

22-O--O-CHCH22-CH-CH

33

An alcohol (Ethanol)

H-C-C-O-H

HH

HH

CH3 N HH

CH3 N H

CH3

CH3 N CH3

CH3

(a 1° amine) (a 2° amine) (a 3° amine)

Common Functional GroupsCommon Functional Groups


Carbonyl group Carbonyl group or unitor unit

AldehydeAldehyde

ketonesketones

Carboxylic acidsCarboxylic acids

O

CH3-C-O-H CH3COOH CH3CO2Hor or

Acetic acid

Common Functional Groups (continued)Common Functional Groups (continued)


Class Functional group Example Classification of organic compoundsClassification of organic compounds

1-1 CHEM 121, Winter 2009, LA TECH Chapter 12. Saturated Hydrocarbons Sections.

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Transcript of 1-1 CHEM 121, Winter 2009, LA TECH Chapter 12. Saturated Hydrocarbons Sections.