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1,2-Dimethylcyclopropane is a cycloalkane consisting of a cyclopropane ring substituted with two methyl groups attached to adjacent carbon atoms. [1] It has three stereoisomers , one cis -isomer and a pair of trans - enantiomers , which differ depending on the orientation of the two methyl groups.
As an example, four of the carbon atoms of the aldohexose class of molecules are asymmetric, therefore the Le Bel–Van 't Hoff rule gives a calculation of 2 4 = 16 stereoisomers. This is indeed the case: these chemicals are two enantiomers each of eight different diastereomers : allose , altrose , glucose , mannose , gulose , idose , galactose ...
For example, 3-methyl-1-pentene with a rectus assignment is formatted as (R)-3-methyl-1-pentene. [12] An example of a (s) descriptor: (1R,2s,3S)-1,2,3-trichlorocyclopentane. A practical method of determining whether an enantiomer is R or S is by using the right-hand rule: one wraps the molecule with the fingers in the direction 1 → 2 → 3.
Stereochemistry, a subdiscipline of chemistry, studies the spatial arrangement of atoms that form the structure of molecules and their manipulation. [1] The study of stereochemistry focuses on the relationships between stereoisomers, which are defined as having the same molecular formula and sequence of bonded atoms (constitution) but differing in the geometric positioning of the atoms in space.
Because (1R,3R)-1,2,3-trimethylcyclopentane is a cycloalkane, its three methyl substituents are capable of exhibiting cis/trans isomerism. This implies that the methyl groups in positions 1,2, and 3 may occupy different spatial arrangements (i.e.they may either lay cis or trans with respect to each other).
For example, dibromocarbene and cis-2-butene yield cis-2,3-dimethyl-1,1-dibromocyclopropane, whereas the trans isomer exclusively yields the trans cyclopropane. [ 4 ] This addition remains stereospecific even if the starting alkene is not isomerically pure, as the products' stereochemistry will match the reactants'.
[2] [3] The term metamer was formerly used for the same concept. [4] For example, butanol H 3 C−(CH 2) 3 −OH, methyl propyl ether H 3 C−(CH 2) 2 −O−CH 3, and diethyl ether (H 3 CCH 2 −) 2 O have the same molecular formula C 4 H 10 O but are three distinct structural isomers. The concept applies also to polyatomic ions with the same ...
The possibilities for different isomers continue to multiply as more stereocenters are added to a molecule. In general, the number of stereoisomers of a molecule can be determined by calculating 2 n, where n = the number of chiral centers in the molecule. This holds true except in cases where the molecule has meso forms.