Chimica organica - organic chemistry

CH CH CH CH CH CHCH

3 2 2 3 3 3

–C H

5 12 CH CH

3 3

CH CH CH CH CH CH CHCH CH CH CCH

3 2 2 2 3 3 2 3 3 3

CH 3

Constitutional Isomers

CH = methane, C H = ethane, C H = propane

4 2 6 3 8

The molecular formula of an alkane with more than three

carbons can give more than one structural isomer

• Compounds that have the same molecular formula but

different structural formulas are constitutional isomers

• For example butane and isobutane

• Both of these alkanes have the molecular formula of C H

4 10

• But their structural formula and arrangement is quite different

Butane

Continuous-Chain or Straight-Chain Structure

Structural C H

4 10

Formula Ball-and-Stick Model

Isobutane (2-methylpropane)

Branched-chain Structure

Structural Formula C H

4 10

Ball-and-Stick

Model

Number of Possible Isomers of Alkanes

• Carbon Atoms can

bond in many

different ways Section 14.3

Multiple Carbon–Carbon Bonds

• Alkenes have a

C-C double bond

• Alkynes have a

C-C triple bond

• Arenes have

special bonds that

are represented

as alternating

single and double

C-C bonds in a

six-membered ring

Substituents in Organic

Compounds Section 14.3

Alkenes

• Members of the alkene group have a double

bond between two carbon atoms.

• One hydrogen atom has been removed from

two adjacent carbon atoms, thereby allowing

the two adjacent carbon atoms to form a

double bond.

• General formula is C H

n 2n

• Begins with ethene (ethylene)

• C H

2 4 Section 14.3

Some Members of the Alkene

Series Section 14.3

Naming Alkenes

• “-ane” suffix for the corresponding alkane is

changed to “-ene” for alkenes.

• A number preceding the name indicates the C

atom on which the double bond starts.

– The carbons are numbered such that the double bond has the lowest number.

• For example, 1-butene and 2-butene Section 14.3

Alkynes

• Members of the alkyne group have a triple

bond between two carbon atoms.

• Two hydrogen atoms have been removed

from each of two adjacent carbon atoms,

thereby allowing the two adjacent carbon

atoms to form a triple bond.

• General formula is C H

n 2n-2

• Begins with ethyne (acetylene)

• C H

2 2 Section 14.3

Some Members of the Alkyne

Series Section 14.3

Functional Groups

• Functional group - collection of atoms at a site

within a molecule with a common bonding pattern

• The group reacts in a typical way, generally

independent of the rest of the molecule

• The functional groups affect the reactions, structure,

and physical properties of every compound in which

they occur

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 C’s bonded to the same O (COC)

• Amine: C bonded to N (CN)

• Thiol: C bonded to SH group (CSH)

• Sulfide: Two C’s bonded to same S (CSC)

• Bonds are polar, with partial positive charge on C (δ+)

and partial negative charge (δ−) on electronegative atom

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

OH

• Carboxylic acid: 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 (δ+)

• Carbonyl O has partial negative charge (δ-).

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

• See Table 3.4 for a list

Types of Alkyl groups

• Classified by the connection site

– 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)

Cycloalkanes

• Cycloalkanes are alkanes that have carbon atoms that

form a ring (called alicyclic compounds)

CH2

• Simple cycloalkanes rings of 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)

cyclobutane cyclopentane cyclohexane

cyclopropane

Reactions of Alkanes, Alkenes and

Alkynes

Chemical reactions of Alkanes

• Called paraffins (low affinity compounds) because they

do not react as most chemicals

• They will burn in a flame, producing carbon dioxide,

water, and heat

• They react with Cl in the presence of light to replace H’s

2

with Cl’s (not controlled)

Alkenes

Addition of Halogens

X

C C + X C C

2 X

Br

Br 2

CH CH CH CH CH CH CHCH Br

3 2 2 3 2 2

Addition of Hydrogen

H

2

CH CH CH CH CH CH CH CH

3 2 2 3 2 2 3

Ni

H

CH H

3 2

C C CH CH CH CH

3 2 2 3

Ni

H CH 3

CH

CH H

3

3 2

C C CH CH CH CH

3 2 2 3

Pt

H H

Addition of Water to Alkenes

OH

H 2

CH CH CH CH

2 2 2 3

H

OH

CH CH CH CH OH

2 3 3 2

Markovnikov Addition

CH -CHBr-CH (1)

δ+ δ- 3 3

HBr

CH -CH=CH

3 2 CH -CH -CH Br (2)

3 2 2

+ CH -CHBr-CH (1)

CH -CH-CH 3 3

3 3

+ Br

H I

CH -CH=CH

3 2 + CH -CH -CH Br (2)

CH -CH -CH 3 2 2

3 2 2

II

H is added to carbon with most H atoms

Br is added to carbon with less H atoms

Aromatic hydrocarbons

Benzene’s Unusual Structure

• All its C-C bonds are the same length: 139 pm —

between single (154 pm) and double (134 pm) bonds

• Electron density in all six C-C bonds is identical

• Structure is planar, hexagonal

• C–C–C bond angles 120°

• Each C is sp and has a p orbital perpendicular to the

2

plane of the six-membered ring