CH 2 - Alkanes and Cycloalkanes

hydrocarbons

molecules containing only carbon and hydrogens

saturated hydrocarbons

only single bonds

• has the maximum amount of hydrogens for the amount of carbons

unsaturated hydrocarbons

contain carbon-carbon double bonds or triple bonds

constitutional isomers

compounds with the same molecular formula but a different connectivity of their atoms

classify carbons based on

number of carbon bonded to each

nomenclature - parent name

the longest carbon chain

nomenclature - substituent

a group bonded to the parent chain

alkyl group

a substituent derived by removal of a hydrogen from an alkane; given the symbol R-

constitutional isomers

same formula, different bonding

cycloalkanes formula

CnH2n ; five and six-membered rings are the most common

bicycloalkane

an alkane containing two rings that share two carbons

conformation

any three-dimensional arrangement of atoms in a molecule that results from rotation about a single bond

newman projection

a way to view a molecule by looking along a carbon-carbon single bond

staggered conformation

a conformation in which the atoms or groups on one carbon are as far apart as possible from the atoms or groups on an adjacent carbon

eclipsed conformation

a conformation in which the atoms or groups of atoms on one carbon are as close as possible to the atoms or groups of atoms on an adjacent carbon

dihedral angle

the angle created by two intersecting planes

torsional strain

higher energy of eclipsed conformation/ lower energy of staggered conformation

steric strain

arises when atoms are forced closer together than their volumes will allow

angle strain

arising from bond angles deviating from ideal values

anti conformation

a conformation about a single bond in which the groups on adjacent carbons lie at a dihedral angle of 180

• energy minimized structure has slightly expanded C-C-C angles and compressed H-C-H angles

cyclic structure strains

angle but can also experience torsional and steric

acyclic strains

torsional and steric only

guache conformation

staggered conformaiton where dihedral angle between methyl groups is 60

cyclopropane strain

angle and torsional strains

• smallest ring, but highest strain

cyclobutane

torsional strain decreases due to puckering, but angle strain increases

cyclopentane

torsional strain decreases again due to puckering

cyclohexane

chain conformation reduced both torsional and angle strains to near zero

a boat conformation is less stable than

a chair confirmation

stereoisomerism

same formula and connectivity BUT different orientation in space (configurations)

• trans/cis

in chair confirmations, both axial substituents is

less stable then both equatorial

cis subsituients conformations

both conformations will have equal stability

• both have one axial and one equatorial

non covalent interactions

• ion-ion

• ion-dipole

• hydrogen bonding

• dipole-dipole

  • dispersion forces

reducing charges decreases

strength

ion-ion interactions are the

strongest

dispersion forces

weakest interactions but all molecules experience this interaction

non covalent in alkanes

dispersion forces only

alkane - strength scales with

size

• larger = more dispersion

• larger alcohols have more dispersion than alcohols

combustion needs

oxygen; usually also needs a spark

combustion

carbon + oxygen → CO2 + H2O