Question

Draw all stereoisomers of 3-methyl-2,4-hexadiene. Position the groups attached to the double bond (120° bond angles) to indicate the stereochemistry. Don't use bold wedges, hashed wedges, or wavy or criss-cross bonds.

Answer 1

Stereoisomerdem ya tarehe It is a form of isomerism in which molecules have same molecular formula and sequence of bonded atoms, but differs in the three-dimensional onlentallon of their atoms in space. buiven compound - 3-methyl-2,4- hexacliene le. CH3- CH Drawing all stereoisomers 1. Char3 c=c3 H 3methyl-2,4€ - hexadiene 3 2. Chan CH3 cal 3-metyl-2,42 - lucradliene 1. 3. Hi (=cas M43 Hy CH3 2 c =c 3-methyl-22,4z-breracliene 7-methyl- z H UW 4. Hy CHA 2 Scach RECHE 3-methyl-22,46 heraliene Total 4 stereoisomers. sing) CI Geometrical isomerism arises due to clifference in polarity of bonds around a given stereo-centrelive.double bond ånd cyclic H a Transsawe group K atereo-caure on opposite CEL I fixed le. side ve this band cannot late (het=0/ Trans isomer X YC HP

ruf Au gi b t Stereo centre. Cis-darme grouss on the same side of the stercocentre Uneto) is isomer beometrical isomar arises due to presence of stereocente. So necessary condition for geometrical isomerism is presence of stereocénbe. This can be understood by falling followind examplen 1. (C-C) single band. Bond relation c a . - - CTG Cond rotation como "Since both above compounds are interchangable due to L-C Single bond potention, there is no stercocentre and above compound to not how geometrical isomersen (rather they show conformatonal isomerisin) and thus are some compound. di (C=C) double bond. 5 C =( " I A 1. A CES (Trans)' abies (cis) ble bond cannot rotate, so it will actas stereo centre and first compound at U not convert into second one. Both will have driften invisible individual existence and thens they both are Joyeriam two different compounds. Elz Nomenclature When the cis-trans fails to apply (due to difference in attachez group on both sides of sterescende), the Elz system is used. Consider following example

Bo t tlz 2 atoms attached with Carlsen I FON T I same as atoms attached with carbon 6. So, here we cannot apply cis-trans rule as in ein-transa fule both carbons on sterescente needs to had some aroms. 20, suppose by any method ( more specifically CIP rule), ce a somehow assign priority to the afom present on carbon, then we can performs the nomenelatene. en By Cip rule, cere found that: 1904 higher Bran Here both carbons have c CH22 eigher Chs 1 prority higher prior group on the y un group angrer pror group on the W H O same side it. 'Zusammen' Z w ill five live. together in lyerman), so od 90 m it is Zu isomer att higher B { H 2 Here both carlons have their Pogroup - cha & higher higher prior group on the oppottle ng more E groep side ice Entgegen' live. Elustii lor si opposite in Geriman), soit se obratiti s E isomer 1 provly group mouc

Cann- ingold Prelog Priority Rule Coop Rule) The cip rule helps to assign priority to the group attached with carbon in organic molecule and their help in finding the stereochemistry of the given molecule. CIP rule helps to assign (R/ s) configuration to chiral (optically active) molecule as well as LE/Z) configuration to double bond (geometrical inomer). es Priority to an atom is assign in following order ( decreasing order) – Rule 1. Atom with highest atomic number on e Example t of ! -a-c-a Priority order - I > Brya YA highest atomic Number lowest atomic Number - Br - - CH3 CENY. Priority - N Y C 4 NY atomic atomic number ist Number is 6. Ruted. If two atoms attached with carbon have same atomic number, then one with higher mass number will have buigher priority. Example qC=C B Priority onder - Br 7 ( By Bl 3 371-c-a35 Priority - 1377 435 F > CH3 Atomic No - 17 17 g 6 mass NO - 37 35 19 l СН3

Rule 3. If there are some atoms attached directly to carbon, then we look for next atom and apply rule 1 and 2. CH Ex. 'BT © s CHz for Co - Priority order - both a and b are identical, so We look for next atom attached to respective carbon ( But Br > H=H .. o competition between first atom of both carbon c > u=4 so Br will have a higher priority for - Priority order - Cac h arel Higher pricity 1. } lower priority @ H Ex- w for Co - Priority order ay H=4 competition c-chy for o prisulty orden- odeyn for priority as and o will compete. (we have to see first priore group of tw with first prior group of c , and second prior group will be competed only when first prior group of both canton is same).

Rule 4 - If an atom A is double bonded with an atom B, then A is treated as being singly bonded with two B atoms. Similarly if an atom A is double bonded with an atom B, then A is treated as being singly bonded with Horse B atom . C-CHg lower to- .C=CH₂ priority - C -CECH c-c -H Ć Ć higher priority - CH₂ to Prioully for coffy-, -CH=che , -CECH и и HC -4 (-H C - C-H и и first atom is same for all 4. So, we look for next com and apply the above 4 rules - so order of priority as per cip rule will be from highest to lowest) - -CECH) -CH=CH2 > = CH g- Hig> - CH3