Document:

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                                                                   EXHIBIT 10.49

December 23, 1999

Mrs. Debra Bergevine
224 Prospect Street
Franklin, MA 02038

Dear Deb:

This letter agreement confirms and explains the terms by which you and Nextera
Enterprises, Inc. (Nextera), have mutually agreed to end your employment at
Nextera. At the outset, it is important to acknowledge that both you and Nextera
have agreed not to make any statements to any third parties which could
reasonably be expected to be harmful to the business or goodwill of each other;
in short, we have resolved to be mutually supportive and respectful of each
other. If asked the reason for your departure, Nextera will respond, when
appropriate, that you resigned to pursue other interests and opportunities.

It is further acknowledged that the terms and conditions outlined in this letter
are confidential and will not be divulged to other employees (current or former)
or third parties with the exception of personally retained legal counsel. Such
action will render this agreement null and void.

Your last day of active employment at Nextera will be December 31, 1999. You
will be entitled to receive salary continuation, at your current salary level,
for a period of six months, extending through June 30, 2000. By signing below
you agree to make yourself available on a reasonable basis to facilitate the
transition of projects during the salary continuation period.

Nextera agrees that effective January 1, 2000 you may work in the management and
technology consulting field performing work similar to Nextera's current
business, but that you shall not solicit or cause to be solicited, or aid in the
solicitation of any past or current client or current employee of Nextera for a
period of one year from the effective date of this letter.

Your enrollment in Nextera's medical and dental plans will continue at normal
premium rates through the salary continuation period ( six months ). You may
elect to continue your healthcare benefits after the salary continuation period
for up to eighteen months in accordance with the provisions of COBRA
(Consolidated Omnibus Budget Reconciliation Act).

Nextera will pay you for any vacation days accrued but unused up to your last
day of active employment. You will not accrue vacation days during the salary
continuation period.

During the salary continuation period, you will not be able to make
contributions to your 401(k) plan. A memo with information concerning your
insurance, your 401(k) account and other matters will be sent to you.

You will be entitled to receive a bonus for the 1999 year, in the amount of
$40,000, payable in the payroll of December 31, 1999.

In addition, Nextera waives its right to repurchase any of your shares of common
stock pursuant to your employment agreement. However, your shares remain subject
to the transfer restrictions imposed on "Founders Interests" in Section 4.5 of
the Stockholders Agreement dated as of August 31, 1998, as amended, to which you
are a party. Nextera will commit to circulate for approval an amendment to the
Stockholders Agreement to the parties thereto to secure a waiver of the
restrictions for resale of these shares, although no assurance can be made that
the waiver will be obtained.
<PAGE>   2
Following your final day of employment with Nextera, you will no longer be
subject to Nextera's insider trading policies, including the requirement to seek
pre-clearance before trading in Nextera securities. However, to the extent you
are aware of material, non-public information concerning Nextera, you must
continue to comply with the securities laws.

You agree fully and finally to waive and release all your rights and claims to
your proportionate share of Nextera's Debentures (approximately $45,545.00) in
return for the cancellation of your loan from Nextera amounting to approximately
$32,901.00 including accrued interest, plus a cash payment from Nextera of
$12,644.00 to make up any difference between these two sums as of December 31,
1999.

You will be entitled to professional outplacement assistance for up to $2,500 of
services actually provided.

In exchange for these benefits, you hereby release Nextera and each of its past,
present and future owners, shareholders, affiliates, subsidiaries, officers,
directors, employees and agents, from any and all claims, causes of action and
liabilities of every name and nature, in any way related to or arising out of
your employment at Nextera, or pursuant to any state, federal or local laws,
regulations, executive orders or common law doctrines, including without
limitation any arising under the Age Discrimination in Employment Act, which you
ever had or might now have as of the date of this agreement.

By signing below, you acknowledge that you have been advised to consult with
your own accountant, legal counsel or other tax advisor regarding the tax
consequence of this letter and the benefits described herein to you, and that
none of Nextera Enterprises, Inc., or any of their affiliates has provided any
tax advice to you.

In signing this agreement, you acknowledge that you have been afforded a period
of not less than 21 days to consider its terms, and have been advised to consult
an attorney. You may waive that period by signing earlier. You may revoke your
acceptance of this agreement within 7 days after your execution thereof, and
this agreement shall not become effective or enforceable until after that
revocation period has expired. If you do not so revoke your acceptance, then
this letter shall take effect as a binding agreement between you and Nextera on
the basis set forth above.

Please indicate your assent to the terms of this letter by signing below, where
indicated, and returning one signed copy to us. By your assent, you agree that
Nextera has no other obligations to you and that you have no claims for any
other matters against Nextera, subject to our compliance with the terms of this
letter. By our agreement to the terms of this letter, Nextera agrees that you
have no other obligations to it and that it has no further claims against you,
subject to your compliance with the terms of this agreement. The obligations of
Nextera relative to your salary continuation and your continued enrollment in
benefit plans during the continuation period are conditional upon our receipt of
your signed consent.

Yours truly,

I agree to the terms of this letter:

Signature:  /s/DEBORAH BERGEVINE
            ------------------------

Date:       December 30, 1999
            ------------------------<PAGE>   1
                                                                   EXHIBIT 10.50

December 31, 1999

Mr. Ronald K. Bohlin
9 Partridge Hill Road
Dover, MA 02030

Dear Ron:

This letter agreement confirms and explains the terms by which you and Nextera
Enterprises, Inc. (Nextera), have mutually agreed to end your employment at
Nextera. At the outset, it is important to acknowledge that both you and Nextera
have agreed not to make any statements to any third parties which could
reasonably be expected to be harmful to the business or goodwill of each other;
in short, we have resolved to be mutually supportive and respectful of each
other. If asked the reason for your departure, Nextera will respond, when
appropriate, that you resigned to pursue other interests and opportunities.

It is further acknowledged that the terms and conditions outlined in this letter
are confidential and will not be divulged to other employees (current or former)
or third parties with the exception of personally retained legal counsel. Any
breach of the preceding sentence will render this agreement null and void.

Your last day of active employment at Nextera will be December 31, 1999, and
except as otherwise provided herein, any employment agreement between you and
Nextera shall terminate on said date. You will be entitled to receive salary
continuation, at the level of $450,000 per year, through June 30, 2000. By
signing below you agree to make yourself available on a reasonable basis to
facilitate the transition of projects during the salary continuation period.

Nextera agrees that effective January 1, 2000 you may work in the management and
technology consulting field performing work similar to Nextera's current
business, but that you shall not solicit or cause to be solicited, or aid in the
solicitation of any past or current client or current employee of Nextera for a
period of one year from the effective date of this letter.

Your enrollment in Nextera's medical and dental plans will continue at normal
premium rates through the salary continuation period ( six months ). You may
elect to continue your healthcare benefits after the salary continuation period
for up to eighteen months in accordance with the provisions of COBRA
(Consolidated Omnibus Budget Reconciliation Act).

Nextera will pay you for any vacation days accrued but unused up to your last
day of active employment (December 31, 1999). You will not accrue vacation days
during the salary continuation period.

During the salary continuation period, you will not be able to make
contributions to your 401(k) plan. A memo with information concerning your
insurance, your 401(k) account and other matters will be sent to you.

You will be entitled to receive a bonus for the 1999 year, in the amount of
$101,000 payable within 15 days of the signing of this agreement.

In addition, Nextera waives its right to repurchase any of your shares of common
stock pursuant to your employment agreement. However, your shares remain subject
to the transfer restrictions imposed on "Founders Interests" in Section 4.5 of
the Stockholders Agreement dated as of August 31, 1998, as amended, to which you
are a party. Nextera will commit to circulate by February 1, 2000 for approval
an amendment to the Stockholders Agreement to the parties thereto to secure a
waiver of the restrictions for resale of these shares, although no assurance can
be made that the waiver will be obtained.

<PAGE>   2
Following your final day of employment with Nextera, you will no longer be
subject to Nextera's insider trading policies, including the requirement to seek
pre-clearance before trading in Nextera securities. However, you must continue
to comply with the securities laws.

You agree fully and finally to waive and release all your rights and claims to
your proportionate share of Nextera's Debentures in return for a cash payment
from Nextera of $32,160 which represents your proportional share of the
principal plus accrued interest in the Debenture with an original maturity of
May 1, 2002, to be paid within 15 days of the signing of this agreement.

You will be entitled to professional outplacement assistance for up to $10,000
of services actually provided.

You will be allowed to keep your laptop computer furnished by Nextera.

In exchange for these benefits, you hereby release Nextera and each of its past,
present and future owners, shareholders, affiliates, subsidiaries, officers,
directors, employees and agents, from any and all claims, causes of action and
liabilities of every name and nature, in any way, directly or indirectly,
related to or arising out of your employment at Nextera, or pursuant to any
state, federal or local laws, regulations, executive orders or common law
doctrines, including without limitation any arising under the Age Discrimination
in Employment Act, which you ever had or might now have as of the date of this
agreement. This agreement does not include a waiver of (1) any rights or claims
which may arise after the date hereof, (2) any rights or claims arising from
breach of this agreement, or (3) Executive's right to indemnification as an
officer of Nextera, as determined by applicable law.

Executive understands that California law includes Civil Code Section 1542 which
says that releases usually do not apply to certain unknown claims. Specifically,
Section 1542 of the California Civil Code states as follows:

      "A GENERAL RELEASE DOES NOT EXTEND TO CLAIMS WHICH THE CREDITOR DOES NOT
      KNOW OR SUSPECT TO EXIST IN HIS FAVOR AT THE TIME OF EXECUTING THE
      RELEASE, WHICH IF KNOWN BY HIM MUST HAVE MATERIALLY AFFECTED HIS
      SETTLEMENT WITH THE DEBTOR."

With full awareness and understanding of the above provisions, Executive hereby
waives any rights he may have under Section 1542, as well as under any other
statutes or common law principles of similar effect. Executive intends to, and
hereby does, release Releases from claims which he does not presently know or
suspect to exist at this time.

By signing below, you acknowledge that you have been advised to consult with
your own accountant, legal counsel or other tax advisor regarding the tax
consequence of this letter and the benefits described herein to you, and that
none of Nextera Enterprises, Inc., or any of their affiliates has provided any
tax advice to you.

In signing this agreement, you acknowledge that you have been afforded a period
of not less than 21 days to consider its terms, and have been advised to consult
an attorney. You may waive that period by signing earlier. You may revoke your
acceptance of this agreement within 7 days after your execution thereof, and
this agreement shall not become effective or enforceable until after that
revocation period has expired. If you do not so revoke your acceptance, then
this letter shall take effect as a binding agreement between you and Nextera on
the basis set forth above.

Please indicate your assent to the terms of this letter by signing below, where
indicated, and returning one signed copy to us. By your assent, you agree that
Nextera has no other obligations to you and that you have no claims for any
other matters against Nextera, subject to our compliance with the terms of this
letter. By our agreement to the terms of this letter, Nextera agrees that you
have no other obligations to it and that it has no further claims against you,
subject to your compliance with the terms of this agreement. The obligations of
Nextera relative to your salary continuation and your continued enrollment in
benefit plans during the continuation period are conditional upon our receipt of
your signed consent.

Yours truly,
<PAGE>   3
/s/STEVEN B. FINK
Steven B. Fink
Chairman and Chief Executive Officer
Nextera Enterprises, Inc.

I agree to the terms of this letter:

Signature:  /s/RONALD K. BOHLIN
            -------------------

Date: January 14, 2000

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