Alkanes, Conformational Analysis and Cycloalkanes: every key term you need (+ practice quiz)
25 flashcard terms for Organic Chemistry I Topic 3, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 15-question quiz — free, no account needed.
A hydrocarbon containing only carbon-carbon and carbon-hydrogen single bonds. Every carbon is sp3 hybridized, and the class is unreactive toward acids, bases, and most polar reagents.
Homologous series
A family of compounds differing by successive methylene units. Physical properties such as boiling point change smoothly along the series while chemical behavior stays essentially constant.
IUPAC parent chain
The longest continuous carbon chain containing the principal functional group. Numbering runs from the end that gives the lowest locant to the highest priority feature.
Alkyl substituent
A branch named by replacing the alkane ending with a suffix indicating attachment. Common examples include methyl, ethyl, isopropyl, and tert-butyl groups on a parent chain.
Primary carbon
A carbon bonded to exactly one other carbon. This classification drives everything from radical stability to whether a substrate reacts by a concerted or stepwise pathway.
Secondary carbon
A carbon bonded to two other carbons. It sits at the crossroads of most mechanism questions because both concerted and carbocation routes remain plausible there.
Tertiary carbon
A carbon bonded to three other carbons. Highly hindered toward backside attack yet excellent at supporting a positive charge or a radical center.
Newman projection
A view straight down one carbon-carbon bond, drawing the front atom as a point and the rear atom as a circle. It makes torsional relationships immediately visible.
Dihedral angle
The torsion angle between substituents on adjacent atoms viewed along their connecting bond. Rotating this angle traces out the full conformational energy profile.
Staggered conformation
An arrangement where front bonds bisect the gaps between rear bonds at a sixty degree torsion. It minimizes electron repulsion and represents an energy minimum.
Eclipsed conformation
An arrangement where front and rear bonds align at a torsion of zero degrees. Repulsion between the aligned bonding pairs makes this an energy maximum.
Torsional strain
The energy cost of eclipsing bonds on adjacent atoms, roughly one kilocalorie per mole for each eclipsed hydrogen pair in ethane at ambient conditions.
Steric strain
Repulsion arising when bulky groups are forced close enough that their electron clouds overlap. It grows sharply with substituent size rather than with simple bond alignment.
Anti conformation
The staggered arrangement placing the two largest groups at a torsion of one hundred eighty degrees. For butane this is the global energy minimum.
Gauche conformation
A staggered arrangement with the two large groups sixty degrees apart. It costs a modest amount of steric energy relative to anti but remains a local minimum.
Angle strain
Energy penalty from compressing bond angles away from the ideal value for a given hybridization. It dominates in three- and four-membered rings.
Chair conformation
The puckered, strain-free shape of a six-membered ring. All neighboring bonds are staggered and all internal angles sit near the tetrahedral value.
Boat conformation
A six-membered ring shape with eclipsing along two bonds and a close contact between the two flagpole positions, making it clearly higher in energy than a chair.
Axial position
A ring substituent pointing roughly parallel to the ring axis, alternating up and down around the ring. Bulky groups here suffer severe crowding.
Equatorial position
A ring substituent pointing outward around the ring perimeter. Large groups strongly prefer this location because it avoids crowding across the ring.
Ring flip
Interconversion between two chair forms that exchanges every axial position for an equatorial one. Bonds are never broken; only torsion angles change.
Diaxial interaction
Crowding between an axial substituent and the axial hydrogens two carbons away on the same face. It is the main energetic cost of placing a group axial.
Conformational preference value
The energy difference favoring the equatorial placement of a given substituent. Tert-butyl has such a large value that it effectively locks a ring in one chair.
Cis and trans ring relationships
Substituents on the same face of a ring are cis and on opposite faces are trans. Which chair is favored depends on how many groups can sit equatorial.
Combustion of hydrocarbons
Complete oxidation to carbon dioxide and water, releasing heat. Comparing heats of combustion for isomers is the classic experimental measure of relative strain.