Document:

Exhibit 4.2 

 

[Form of Unit Certificate]

 

NUMBER
UNITS

U-

 

SEE REVERSE FOR CERTAIN
DEFINITIONS

CUSIP [                  ]

 

TORTOISEECOFIN ACQUISITION CORP. III

 

UNITS CONSISTING OF ONE CLASS A ORDINARY SHARE
AND

ONE-FOURTH OF ONE REDEEMABLE WARRANT TO PURCHASE ONE CLASS A ORDINARY SHARE

 

THIS CERTIFIES THAT                                       
is the owner of                                                       Units.

 

Each Unit (“Unit”) consists
of one (1) Class A ordinary share, par value $0.0001 per share (each, a “Class A Ordinary Share”), of TortoiseEcofin
Acquisition Corp. III, a Cayman Islands exempted company (the “Company”), and one-fourth of one redeemable warrant
(each whole warrant, a “Warrant”). Each Warrant entitles the holder to purchase one (1) Class A Ordinary Share
(subject to adjustment) for $11.50 per share (subject to adjustment). Only whole Warrants are exercisable. Each Warrant will become exercisable
thirty (30) days after the Company’s completion of a merger, amalgamation, share exchange, asset acquisition, share purchase, reorganization
or other similar business combination with one or more businesses or entities (each a “Business Combination”)
and will expire unless exercised before 5:00 p.m., New York City Time, on the date that is five (5) years after the date on which the
Company completes its initial Business Combination, or earlier upon redemption or liquidation (the “Expiration Date”).
The Class A Ordinary Shares and Warrants comprising the Units represented by this certificate are not transferable separately prior to
               , 2021, unless Barclays Capital Inc. and Goldman
Sachs & Co. LLC elect to allow earlier separate trading, subject to the Company’s filing of a Current Report on Form 8-K with
the Securities and Exchange Commission containing an audited balance sheet reflecting the Company’s receipt of the gross proceeds
of the offering and issuing a press release announcing when separate trading will begin. No fractional warrants will be issued upon separation
of the Units. The terms of the Warrants are governed by a Warrant Agreement, dated as of                ,
2021, between the Company and Continental Stock Transfer & Trust Company, as Warrant Agent, and are subject to the terms and provisions
contained therein, all of which terms and provisions the holder of this certificate consents to by acceptance hereof. Copies of the Warrant
Agreement are on file at the office of the Warrant Agent at 1 State Street, 30th Floor, New York, New York 10004, and are available to
any Warrant holder on written request and without cost.

 

Upon the consummation of a Business Combination,
the Units represented by this certificate will automatically separate into the Class A Ordinary Shares and Warrants comprising such Units.

 

This certificate is not valid unless countersigned
by the Transfer Agent and Registrar of the Company.

 

This certificate shall be governed by and construed
in accordance with the internal laws of the State of New York.

 

Witness the facsimile signature of its duly authorized
officers.

 

	 	 	 
	Secretary	 	Chief Executive Officer

 

     

     

    

 

TortoiseEcofin Acquisition Corp. III

 

The Company will furnish without charge to each
unitholder who so requests, a statement of the powers, designations, preferences and relative, participating, optional or other special
rights of each class of shares or series thereof of the Company and the qualifications, limitations or restrictions of such preferences
and/or rights.

 

The following abbreviations, when used in the
inscription on the face of this certificate, shall be construed as though they were written out in full according to applicable laws or
regulations:

 

	TEN COM	–	as tenants in common	 	UNIF GIFT MIN ACT	–	 ___________ Custodian ___________
	TEN ENT	–	as tenants by the entireties	 	 	 	(Cust)                                    (Minor)
	 	 	 	 	 	 	 
	JT TEN	–	as joint tenants with right of survivorship and not as tenants in common	 	 	 	
    under Uniform Gifts to Minors Act

    ________________________________

    (State)

  

Additional abbreviations may also be used though
not in the above list.

 

For value received,                          
hereby sell, assign and transfer unto                                             

 

 

 

PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING
NUMBER OF ASSIGNEE

 

 

 

(PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING
ZIP CODE, OF ASSIGNEE)

 

 

 

 

 

 

 

 

Units represented by the within Certificate, and do hereby irrevocably
constitute and appoint Attorney to transfer the said Units on the books of the within named Company with full power of substitution in
the premises.

 

	Dated:	 	 	 	 
	 	 	 	 	 
	 	 	 	 	 
		 		Notice:	The signature to this assignment must correspond with the name as written upon the face of the certificate in every particular, without alteration or enlargement or any change whatever.

 

	Signature(s) Guaranteed:	 
	 	 
	THE SIGNATURE(S) MUST BE GUARANTEED BY AN ELIGIBLE GUARANTOR INSTITUTION (BANKS, STOCKBROKERS, SAVINGS AND LOAN ASSOCIATIONS AND CREDIT UNIONS WITH MEMBERSHIP IN AN APPROVED SIGNATURE GUARANTEE MEDALLION PROGRAM, PURSUANT TO THE U.S. SECURITIES AND EXCHANGE COMMISSION RULE 17Ad-15 (OR ANY SUCCESSOR RULE)) UNDER THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.	 

 

In each case, as more fully described in the Company’s
final prospectus dated           , 2021, the holder(s) of this certificate shall be entitled to receive a pro-rata portion of certain funds held
in the trust account established in connection with the Company’s initial public offering only in the event that (i) the Company
redeems the Class A Ordinary Shares sold in its initial public offering and liquidates because it does not consummate an initial Business
Combination within the period of time set forth in the Company’s amended and restated memorandum and articles of association, as
the same may be amended from time to time (the “Memorandum and Articles”), (ii) the Company redeems the Class
A Ordinary Shares sold in its initial public offering in connection with a shareholder vote to approve an amendment to the Memorandum
and Articles that would affect (A) the substance or timing of the Company’s obligation to redeem 100% of the Class A Ordinary Shares
if it does not consummate an initial Business Combination within the time period set forth therein or (B) any other provision relating
to the rights of holders of Class A Ordinary Shares or (iii) if the holder(s) seek(s) to redeem for cash his, her or its respective Class
A Ordinary Shares in connection with a tender offer (or proxy solicitation, solely in the event the Company seeks shareholder approval
of the proposed initial Business Combination) setting forth the details of a proposed initial Business Combination. In no other circumstances
shall the holder(s) have any right or interest of any kind in or to the trust account.Exhibit 4.3

 

[Form of Warrant Certificate]

 

[FACE]

 

Number

 

Warrants

 

 

 

THIS WARRANT SHALL BE NULL AND VOID IF NOT
EXERCISED PRIOR TO

THE EXPIRATION OF THE EXERCISE PERIOD PROVIDED FOR

IN THE WARRANT AGREEMENT DESCRIBED BELOW

 

TORTOISEECOFIN ACQUISITION CORP. III

Incorporated Under the Laws of the Cayman Islands

 

CUSIP [            ]

 

Warrant Certificate

 

This Warrant Certificate certifies that
          , or registered assigns, is the registered holder of           
warrant(s) evidenced hereby (the “Warrants” and each, a “Warrant”) to purchase Class
A ordinary shares, $0.0001 par value per share (“Ordinary Shares”), of TortoiseEcofin Acquisition Corp. III,
a Cayman Islands exempted company (the “Company”). Each Warrant entitles the holder, upon exercise during the
period set forth in the Warrant Agreement referred to below, to receive from the Company that number of fully paid and non-assessable
Ordinary Shares as set forth below, at the exercise price (the “Exercise Price”) as determined pursuant to the
Warrant Agreement, payable in lawful money of the United States of America (or through “cashless exercise” as
provided for in the Warrant Agreement) upon surrender of this Warrant Certificate and payment of the Exercise Price at the office or agency
of the Warrant Agent referred to below, subject to the conditions set forth herein and in the Warrant Agreement. Defined terms used in
this Warrant Certificate but not defined herein shall have the meanings given to them in the Warrant Agreement.

 

Each whole Warrant is initially exercisable for
one fully paid and non-assessable Ordinary Share. Fractional shares of ordinary shares shall not be issued upon exercise of any Warrant.
If, upon the exercise of Warrants, a holder would be entitled to receive a fractional interest in an Ordinary Share, the Company shall,
upon exercise, round down to the nearest whole number of Ordinary Shares to be issued to the warrantholder. The number of Ordinary Shares
issuable upon exercise of the Warrants is subject to adjustment upon the occurrence of certain events as set forth in the Warrant Agreement.

 

The initial Exercise Price is equal to $11.50
per Ordinary Share. The Exercise Price is subject to adjustment upon the occurrence of certain events as set forth in the Warrant Agreement.

 

Subject to the conditions set forth in the Warrant
Agreement, the Warrants may be exercised only during the Exercise Period and to the extent not exercised by the end of such Exercise Period,
such Warrants shall become void. The Warrants may be redeemed, subject to certain conditions, as set forth in the Warrant Agreement.

 

Reference is hereby made to the further provisions
of this Warrant Certificate set forth on the reverse hereof and such further provisions shall for all purposes have the same effect as
though fully set forth at this place.

 

This Warrant Certificate shall not be valid unless
countersigned by the Warrant Agent, as such term is used in the Warrant Agreement.

 

    1

     

    

 

This Warrant Certificate shall be governed by
and construed in accordance with the internal laws of the State of New York, without regard to conflicts of laws principles thereof.

 

	 	TORTOISEECOFIN ACQUISITION CORP. III
	 	 
	 	By:	 
	 	 	Name: 
	 	 	Title:
	 	 	 
	 	CONTINENTAL STOCK TRANSFER
	 	& TRUST COMPANY, as Warrant Agent
	 	 
	 	By:	 
	 	 	Name: 
	 	 	Title:

 

    2

     

    

 

[Form of Warrant Certificate]

 

[Reverse]

 

The Warrants evidenced by this Warrant Certificate
are part of a duly authorized issue of Warrants entitling the holder on exercise to receive Ordinary Shares and are issued or to be issued
pursuant to a Warrant Agreement dated as of           , 2021 (the “Warrant
Agreement”), duly executed and delivered by the Company to Continental Stock Transfer & Trust Company, a New York corporation,
as warrant agent (the “Warrant Agent”), which Warrant Agreement is hereby incorporated by reference in and made
a part of this instrument and is hereby referred to for a description of the rights, limitation of rights, obligations, duties and immunities
thereunder of the Warrant Agent, the Company and the holders (the words “holders” or “holder”
meaning the Registered Holders or Registered Holder, respectively) of the Warrants. A copy of the Warrant Agreement may be obtained by
the holder hereof upon written request to the Company. Defined terms used in this Warrant Certificate but not defined herein shall have
the meanings given to them in the Warrant Agreement.

 

Warrants may be exercised at any time during the
Exercise Period set forth in the Warrant Agreement. The holder of Warrants evidenced by this Warrant Certificate may exercise them by
surrendering this Warrant Certificate, with the form of election to purchase set forth hereon properly completed and executed, together
with payment of the Exercise Price as specified in the Warrant Agreement (or through “cashless exercise” as
provided for in the Warrant Agreement) at the principal corporate trust office of the Warrant Agent. In the event that upon any exercise
of Warrants evidenced hereby the number of Warrants exercised shall be less than the total number of Warrants evidenced hereby, there
shall be issued to the holder hereof or his, her or its assignee, a new Warrant Certificate evidencing the number of Warrants not exercised.

 

Notwithstanding anything else in this Warrant
Certificate or the Warrant Agreement, no Warrant may be exercised unless at the time of exercise (i) a registration statement covering
the Ordinary Shares to be issued upon exercise is effective under the Securities Act and (ii) a prospectus thereunder relating to the
Ordinary Shares is current, except through “cashless exercise” as provided for in the Warrant Agreement.

 

The Warrant Agreement provides that upon the occurrence
of certain events the number of Ordinary Shares issuable upon exercise of the Warrants set forth on the face hereof may, subject to certain
conditions, be adjusted. If, upon exercise of a Warrant, the holder thereof would be entitled to receive a fractional interest in an Ordinary
Share, the Company shall, upon exercise, round down to the nearest whole number of Ordinary Shares to be issued to the holder of the Warrant.

 

Warrant Certificates, when surrendered at the
principal corporate trust office of the Warrant Agent by the Registered Holder thereof in person or by legal representative or attorney
duly authorized in writing, may be exchanged, in the manner and subject to the limitations provided in the Warrant Agreement, but without
payment of any service charge, for another Warrant Certificate or Warrant Certificates of like tenor evidencing in the aggregate a like
number of Warrants.

 

Upon due presentation for registration of transfer
of this Warrant Certificate at the office of the Warrant Agent a new Warrant Certificate or Warrant Certificates of like tenor and evidencing
in the aggregate a like number of Warrants shall be issued to the transferee(s) in exchange for this Warrant Certificate, subject to the
limitations provided in the Warrant Agreement, without charge except for any tax or other governmental charge imposed in connection therewith.

 

The Company and the Warrant Agent may deem and
treat the Registered Holder(s) hereof as the absolute owner(s) of this Warrant Certificate (notwithstanding any notation of ownership
or other writing hereon made by anyone), for the purpose of any exercise hereof, of any distribution to the holder(s) hereof, and for
all other purposes, and neither the Company nor the Warrant Agent shall be affected by any notice to the contrary. Neither the Warrants
nor this Warrant Certificate entitles any holder hereof to any rights of a shareholder of the Company.

 

    3

     

    

 

Election to Purchase

 

(To Be Executed Upon Exercise of Warrant)

 

The undersigned hereby irrevocably elects to
exercise the right, represented by this Warrant Certificate, to receive           
Ordinary Shares and herewith tenders payment for such Ordinary Shares to the order of
            TortoiseEcofin Acquisition Corp. III (the
“Company”) in the amount of $           in accordance
with the terms hereof. The undersigned requests that the register of members of the Company be updated to reflect the issuance of
such Ordinary Shares and a certificate for such Ordinary Shares be registered in the name of
          , whose address is
           and that such Ordinary Shares be delivered to
           whose address is
          . If said number of Ordinary Shares is less than all of the Ordinary
Shares purchasable hereunder, the undersigned requests that a new Warrant Certificate representing the remaining balance of such
Ordinary Shares be registered in the name of           , whose address is
           and that such Warrant Certificate be delivered to
          , whose address is
          .

 

In the event that the Warrant has been called
for redemption by the Company pursuant to Section 6 of the Warrant Agreement and the Company has required cashless exercise pursuant
to Section 6.3 of the Warrant Agreement, the number of Ordinary Shares that this Warrant is exercisable for shall be determined
in accordance with subsection 3.3.1(b) and Section 6.3 of the Warrant Agreement.

 

In the event that the Warrant is a Private Placement
Warrant that is to be exercised on a “cashless” basis pursuant to subsection 3.3.1(c) of the Warrant
Agreement, the number of Ordinary Shares that this Warrant is exercisable for shall be determined in accordance with subsection 3.3.1(c)
of the Warrant Agreement.

 

In the event that the Warrant is to be exercised
on a “cashless” basis pursuant to Section 7.4 of the Warrant Agreement, the number of Ordinary Shares
that this Warrant is exercisable for shall be determined in accordance with Section 7.4 of the Warrant Agreement.

 

In the event that the Warrant may be exercised,
to the extent allowed by the Warrant Agreement, through cashless exercise (i) the number of Ordinary Shares that this Warrant is exercisable
for would be determined in accordance with the relevant section of the Warrant Agreement which allows for such cashless exercise and (ii)
the holder hereof shall complete the following:

 

The undersigned hereby irrevocably elects to exercise
the right, represented by this Warrant Certificate, through the cashless exercise provisions of the Warrant Agreement, to receive          Ordinary
Shares. If said number of Ordinary Shares is less than all of the Ordinary Shares purchasable hereunder (after giving effect to the cashless
exercise), the undersigned requests that a new Warrant Certificate representing the remaining balance of such Ordinary Shares be registered
in the name of           , whose address is           
and that such Warrant Certificate be delivered to           , whose address is           .

 

[Signature Page Follows]

 

    4

     

    

 

Date:         , 20

 

	 	 
	 	(Signature)
	 	 
	 	 
	 	 
	 	 
	 	(Address)
	 	 
	 	 
	 	(Tax Identification Number)

Signature Guaranteed:

 

 

THE SIGNATURE(S) SHOULD BE GUARANTEED BY AN ELIGIBLE GUARANTOR INSTITUTION
(BANKS, STOCKBROKERS, SAVINGS AND LOAN ASSOCIATIONS AND CREDIT UNIONS WITH MEMBERSHIP IN AN APPROVED SIGNATURE GUARANTEE MEDALLION PROGRAM,
PURSUANT TO THE U.S. SECURITIES AND EXCHANGE COMMISSION RULE 17Ad-15 (OR ANY SUCCESSOR RULE)) UNDER THE SECURITIES EXCHANGE ACT OF 1934,
AS AMENDED.

 

 

 

5

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