Organic 2: Alkanes & Cycloalkanes - Intro to Hydrocarbons Flashcards
Hydrocarbons
2 classes - alliphatic & aromatic
Alkanes
hydrocarbons in which all the bonds are single bonds; general formula = CnH2n+2
Alkenes
hydrocarbons with at least one carbon-carbon double bond
Alkynes
hydrocarbons with at least one carbon-carbon triple bond
Arenes
another name for aromatic hydrocarbons
Benzene
most important aromatic hydrocarbon
Constructive interference
occurs when 2 waves combine so as to reinforce each other (in phase)
Destructive interference
occurs when 2 waves oppose each other (out of phase)
Valence Bond Model
bases the connection between 2 atoms on the overlap between half-filled orbitals of the 2 atoms; pictures a covalent bond between 2 atoms in terms of an in-phase overlap of a half-filled orbital of 1 atom with a half-filled orbital of the other
Molecular Orbital Model
assembles a set of molecular orbitals by combining the atomic orbitals of all of the atoms in the molecule; rests on the notion that, as electrons in atoms occupy atomic orbitals, electrons in molecules occupy molecular orbitals
Sigma bond
a bond in which the orbitals overlap along a line connecting the atoms (the internuclear axis); electron distribution is cylindrically symmetrical
Linear Combination of Atomic Orbitals-Molecular Orbital Method (LCAO-MO)
representing molecular orbitals as combinations of atomic orbitals
Bonding Orbital
the additive combination (of 2 wave functions)
Antibonding Orbital
the subtractive combination (of 2 wave functions)
Alkane Boiling Point Rule
as the number of carbon atoms increases, so does the boiling point
Sp3 hybrid orbitals
4 new orbitals coming from 1 s orbital and 3 p orbitals
Methyl groups
the group -CH3
n-butane
four carbons are joined in a continuous chain; n = normal (carbon chain is unbranched)
Isobutane
common name for 2-methylpropane (CH3)3CH; 2nd isomer - has a branched carbon chain
Methylene
-CH2 group
Methine
-CH group
Homologous series
series in which successive members differ by a -CH2- group
IUPAC rules
International Union of Pure and Applied Chemistry; alkane names form the foundation of the system
Common names
names not derived from a set of rules
Systematic names
names derived according to a prescribed set of rules
Preferred IUPAC Name (PIN)
2004 IUPAC recommendations established this concept suitable for use in formal communications (patents, international commerce, occupational health/safety, environmental regulation, etc); distinguished from “general” IUPAC names
Generic drug names
not derived from systematic nomenclature; US Adopted Names Council (USAN), a private organization founded by the American Medical Association, the American Pharmacists Association, and the US Pharmacopeial Convention; International Proprietary Names (INN) are designated by the World Health Organization
Locants
in IUPAC nomenclature, a prefix that designates the atom that is associated with a particular structural unit; most often a number; structural unit is usually an attached substituent as in 2-chlorobutane
Alkyl group
lacks one of the hydrogens of an alkane
Primary carbon
a carbon directly attached to one other carbon
Secondary carbon
a carbon directly attached to 2 other carbons
Tertiary carbon
a carbon directly attached to 3 other carbons
Quaternary carbon
a carbon directly attached to 4 other carbons
Cycloalkanes
alkanes that contain a ring of 3 or more carbons
Refining
conversion of crude oil to useful materials, especially gasoline
Cracking
increases the proportions of hydrocarbons at the expense of higher-molecular-weight ones by processes that involve the cleavage of carbon-carbon bonds induced by head (thermal ____) or with the aid of certain catalysts (catalytic ____)
Reforming
converts the hydrocarbons in petroleum to aromatic hydrocarbons and highly branched alkanes, both of which show less tendency for knocking than unbranched alkanes and cycloalkanes
Intermolecular attractive forces
forces, either attractive or repulsive, between 2 atoms or groups in separate molecules; greater in the liquid than in the gas phase
van der Waals forces
intermolecular forces that do not involve ions (dipole-dipole, dipole/induced-dipole, and induced-dipole/induced-dipole forces)
Induced-dipole/induced-dipole attractive force
force of attraction resulting from a mutual and complementary polarization of one molecule by another; also referred to as London forces or dispersion forces
van der Waals radius
distance of closest approach characteristic
Hydrophobic effect
the exclusion of nonpolar molecules, such as alkanes, from water
Paraffin hydrocarbons
older name for alkanes; “with little affinity” - testifies to the low level of reactivity of alkanes
Combustion
burning in air is the best known and most important example of alkanes participating in redox reactions; exothermic, gives CO2 and H20 as products
Heat of combustion
heat released on combustion of a substance
Enthalpy
heat content of a compound in its standard state
Heat of formation
enthalpy change for formation of 1 mole of a compound directly from its elements; 1 type of heat of reaction
Potential energy
comparable with enthalpy; it is the energy a molecule has exclusive of its kinetic energy; a molecule with more of this is less stable than an isomer with less of this
Intramolecular forces
forces, either attractive or repulsive, between 2 atoms or groups within the same molecule
Oxidation-reduction
a reaction in which an electron is transferred from 1 atom to another so that each atom undergoes a change in oxidation number
Oxidation number (oxidation state)
the formal charge an atom has when the atoms in its covalent bonds are assigned to the more electronegative partner
Sp2 hybrid orbitals
mixing the 2s orbital with 2 of the 2p orbitals; 1 of the 2p orbitals is left unhybridized
Pi bond
a bond in which the electron distribution is concentrated above and below the internuclear axis, rather than along it as in a sigma bond; most often associated with a side-by-side overlap of p orbitals on adjacent atoms that are already connected by a sigma bond
Pi electrons
electrons in a pi bond; probability of finding one of these is highest in the region above and below the plane of the molecule
sp hybridization
applies when carbon is directly bonded to 2 atoms (ex. acetylene)
